Method and apparatus for making shoe lasts and/or shoe components

What is claimed is:

1. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or more graded last digital files each representing a different last size of the respective shoe style;

and utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style.

2. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or more graded last digital files each representing a different last size of the respective shoe style;

and utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style.

wherein the outer surface of the model last is digitized by a tracer probe which is spring-urged into contact with the outer surface of the model last as the model last is continuously rotated about its longitudinal axis and as the tracer probe is advanced parallel to the longitudinal axis of the model last.

3. The method according to claim 2, wherein the digitizing operation measures the instantaneous position of the tracer probe at each sample point to represent the tool path points at the three-dimensional surface contour of the respective model last; and the grading step converts said tool path points to surface points of the model last, grades said surface points to represent different lengths and widths of lasts of the respective shoe style, and then reconverts said graded surface points to graded tool path points in the graded digital files.

4. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or more graded last digital files each representing a different last size of the respective shoe style;

and utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style.

wherein the outer surface of the model last is digitized by an optical device directing an optical beam against the outer surface of the model last as the model last is continuously rotated about its longitudinal axis and as the optical beam is advanced parallel to the longitudinal axis of the model last.

5. The method according to claim 4, wherein the digitizing operation directly measures the surface points on the model last, and the grading step grades said surface points to represent different lengths and widths of lasts of the respective shoe style, and then converts said graded surface points to graded tool path points in the graded digital files.

6. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or more graded last digital files each representing a different last size of the respective shoe style;

utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style;

digitizing a large number of sample points on the feather line of the model last to produce a feather line digital file representing the feather line of the respective model last;

and utilizing said feather line digital file, together with said model last digital file, for producing said one or more graded last digital files of the respective shoe style.

7. The method according to claim 6, wherein the outer surface of the model last is digitized by a tracer probe which is spring-urged into contact with the outer surface of the model last as the model last is continuously rotated about its longitudinal axis and as the tracer probe is advanced parallel to the longitudinal axis of the model last.

8. The method according to claim 7, wherein the model last is of electrically-insulating material except for its bottom which is of electrically-conductive material, and wherein said spring-urged tracer probe is of electrically-conductive material, such that the juncture line of the last bottom with the remainder of the last, constituting said feather line, is electrically sensed by said spring-urged tracer probe.

9. The method according to claim 7, wherein the sides of the model last have one optical characteristic and its bottom has another optical characteristic, and the juncture line of the last bottom with the remainder of the last, constituting said feather line, is optically sensed.

10. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or more graded last digital files each representing a different last size of the respective shoe style;

utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style;

digitizing a large number of sample points on preselected style-lines of the model last to produce a style-line digital file for the respective shoe style;

and utilizing said style-line digital file, together with said model last digital file, for producing one or more graded component digital files each representing a different component size of the respective shoe style.

11. The method according to claim 10, wherein said one or more graded component digital files is produced by defining, from the style-lines in said style-line digital file, one or more shoe components each bounded by at least three style-lines;

grading said model last digital file to produce one or more graded last digital files each representing a different size of the respective shoe style;

extracting from each of said graded last digital files the digital data corresponding to each of said shoe components defined by said at least three style-lines to produce graded component digital data representing the configuration of the respective component in three dimensions;

and converting said three-dimensional graded component digital data to digital data representing said graded component in two dimensions.

12. The method according to claim 10, wherein said preselected style-lines are digitized by an optical device which directs an optical beam against the outer surface of the model last as the model last is continuously rotated about its longitudinal axis and as the optical beam is advanced parallel to the longitudinal axis of the model last.

13. A method of making shoe components, comprising:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

digitizing a large number of sample points on preselected style-lines of the model last to produce a style-line digital file for the respective shoe style;

defining, from the data in said style-line digital file, one or more shoe components each bounded by at least three style-lines;

grading said model last digital file to produce one or more graded last digital files each representing a different size of the respective shoe style;

extracting from each of said graded last digital files the digital data corresponding to each of said shoe components defined by said at least three style-lines to produce graded component digital data representing the three-dimensional configuration of the respective component;

converting said three-dimensional graded component digital data to the two-dimensional configuration of the respective component; and

utilizing said two-dimensional graded component digital data to cut the respective components.

14. A method of making shoe components, comprising:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

digitizing a large number of sample points on preselected style-lines of the model last to produce a style-line digital file for the respective shoe style;

defining, from the data in said style-line digital file, one or more shoe components each bounded by at least three style-lines;

grading said model last digital file to produce one or more graded last digital files each representing a different size of the respective shoe style;

extracting from each of said graded last digital files the digital data corresponding to each of said shoe components defined by said at least three style-lines to produce graded component digital data representing the three-dimensional configuration of the respective component;

converting said three-dimensional graded component digital data to the two-dimensional graded component digital data to the two-dimensional configuration of the respective component; and

utilizing said two-dimensional graded component digital data to cut the respective components,

wherein said preselected style-lines are digitized by an optical device which directs an optical beam against the outer surface of the model last as the model last is continuously rotated about its longitudinal axis and as the optical beam is advanced parallel to the longitudinal axis of the model last.

15. A method of making shoe lasts, comprising the operations:

digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

grading said model last digital file to produce one or

more graded last digital files each representing a different last size of the respective shoe style;

and utilizing each of said graded last digital files to produce a graded shoe last of the respective shoe style,

wherein said grading operation includes the steps:

displaying on a screen one or more of said graded lasts;

manipulating the displayed graded last and modifying its configuration so as to disproportionately change at least one of its dimensions with respect to other dimensions;

and utilizing the so modified configuration of the displayed graded last to produce the respective graded last digital file.

16. Apparatus for use in making shoe lasts, comprising:

rotary drive means for rotating a model last representing a particular shoe style;

digitizing means for digitizing a large number of sample points on the outer surface of said model last to produce a model last digital file representing the three-dimensional surface contour of the respective model last;

and grading means for producing from said model last digital file a plurality of graded last digital files representing different lengths and widths of lasts of the respective shoe style.

17. The appararatus according to claim 16, wherein said digitizing means comprises:

a tracer probe;

rotary drive means for rotating said model last about its longitudinal axis, constituting a first axis;

a first encoder producing an electrical output representing the instantaneous angular position of the model last about said first axis;

a spring urging said tracer probe along a second axis in contact with the outer surface of the model last as the model last is rotated by said rotary drive means about said first axis;

a second encoder producing an electrical output representing the instantaneous position of said tracer probe along said second axis;

linear drive means for driving said tracer probe along a third axis parallel to said first axis;

and a third encoder producing an electrical output representing the instantaneous linear position of the tracer probe along said third axis.

18. The apparatus according to claim 17, wherein said tracer probe is a wheel rollable along the outer surface of the model last while spring-urged into contact therewith.

19. The apparatus according to claim 16, wherein said digitizing means also digitizes a large number of sample points on the feather line of the model last to produce a feather line digital file representing the feather line of the respective model last; and said grading means also utilizes said feather line digital file, together with said model last digital file, for producing said plurality of graded last digital files of the respective shoe style.

20. The apparatus according to claim 19, wherein said model last is of electrically-insulating material except for its bottom, which is of electrically-conductive material; and said digitizing means includes an electrically-conductive probe which is spring-urged into contact with the outer surface of the model last to electrically sense the juncture line of the last bottom with the remainder of the last, said juncture line constituting said feather line.

21. The apparatus according to claim 20, wherein said probe is an electrically-conductive wheel rollable along the outer surface of the model last while spring-urged into contact therewith.

22. The apparatus according to claim 21, wherein said digitizing means further comprises:

a first encoder producing an electrical output representing the instantaneous position of said tracer probe along said first axis;

a second encoder producing an electrical output representing the instantaneous angular position of the model last about said second axis;

linear drive means for driving said tracer probe along a third axis parallel to said second axis;

and a third encoder producing an electrical output representing the instantaneous linear position of the tracer probe along said third axis.

23. The apparatus according to claim 19, wherein said model last has one optical characteristic except for its bottom which has another optical characteristic, and said digitizing means comprises an optical sensor for sensing the juncture line, constituting said feather line, of the bottom of the last with the remainder of the last.

24. The apparatus according to claim 16, wherein said digitizing means comprises an optical device directing an optical beam against the outer surface of the model last as the model last is rotated about its longitudinal axis.

25. The apparatus according to claim 16, wherein said model last includes a plurality of stylelines, and said digitizing means includes style-line digitizing means for digitizing a large number of sample points on said style-lines to produce a styleline digital file for the respective shoe style; and wherein said grading means also includes means enabling extraction from said model last digital file the digital data defining one or more shoe components each identified by at least three lines from said style-line digital file; and means for converting said extracted digital data, representing the three-dimensional configuration of the respective graded component, to correspond to the two-dimensional configuration thereof.

26. The apparatus according to claim 25, wherein said style-line digitizing means includes an optical device which directs an optical beam against the outer surface of the model last as the model last is continuously rotated about its longitudinal axis.

27. Apparatus for use in making components of shoes, comprising:

rotary drive means for rotating a model last, representing a particular shoe style, about its longitudinal axis which model last includes a plurality of style-lines;

digitizing means for digitizing a large number of sample points on the outer surface of the model last to produce a model last digital file representing the three-dimensional surface configuration of the respective model last, and for digitizing a large number of sample points on the style-lines to produce a style-line digital file for the respective style-line;

and grading means utilizing said model last digital file for producing a plurality of graded last digital files representing different last sizes of the respective shoe style;

said grading means including means enabling extraction from said model last digital file the digital data defining one or more shoe components each identified by at least three lines from said style-line digital file; and means for converting said extracted digital data, representing the three-dimensional configuration of the respective graded component, to correspond to the two-dimensional configuration thereof.

28. The apparatus according to claim 27, wherein said digitizing means includes an optical device which directs an optical beam against the outer surface of the model last as the model last is continuously rotated about its longitudinal axis to sense said style-lines and to produce said style-line digital file.

29. The apparatus according to claim 16, wherein said grading means includes:

a display for displaying the graded lasts;

manipulatable means enabling the operator to manipulate the graded lasts displayed and to modifiy its outer configuration so as to disproportionately change at least one of its dimensions with respect to others of its dimensions;

and computer means for modifying the digital data of the graded last to correspond to the modified configuration of the graded last.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates to a method and to an apparatus for making shoe lasts and/or components for shoes.

A shoe last is a block or form shaped like a human foot used in manufacturing shoes and also in repairing shoes. In the manufacture of shoes, a model last is produced for each particular shoe last style, and then a plurality of graded lasts are produced according to the different lengths and widths to be made available for the respective shoe style.

The grading procedure is usually not a straightforward one wherein all dimensions are proportionately increased with the increase in size; rather, to avoid distortions, and also to minimize the initial tooling costs (e.g., moulds) required to manufacture the shoe components, many dimensions are not increased, or are disproportionately increased, for a plurality of grades. For example, "bottom-holding", "heel-height holding", "toe-spring holding", and "toe-thickness holding" techniques are frequently used in order to maintain certain dimensions for a plurality of sizes, or to change the dimensions in a non-linear manner with respect to the different sizes.

An important factor of the respective syle influencing the grading procedure is the feather line of the model last, namely the juncture line of the last bottom with the last sides. The feather line determines the outer configuration of the last bottom and is frequently involved in these "holding" techniques.

Generally speaking, producing graded lasts from a model last not only requires a high degree of expertise and experience, but also is very expensive and time-consuming. According to present techniques, a model last for each style is first produced by an artisan model-maker, and then the graded lasts, corresponding to the different sizes of the same basic style, are usually prepared by a pantograph machine, in which the different sizes are produced by adjusting the arms of the pantograph. However, this method produces considerable distortions which are cumulative; that is, a distortion from one size to the next may not be too significant, but they become very significant when they are magnified by differences in three or four sizes. These distortions therefore require considerable "retouching" by the last maker; moreover, they limit the variations possible as a practical matter in the different grades.

The components (e.g., the flat leather, plastic, fabric blanks for making the sides, soles, heels, etc.) used in manufacturing the shoe are uusually indicated by style-lines marked on the model last. These style-lines also indicate the stitching lines of the various components used in the manufacture of the shoes, and thereby the configurations of such components. Techniques are known for converting the three-dimensional configuration of a shoe component, as determined by three or more style-lines on the shoe last, to a two-dimensional configuration for manufacturing the respective components. However, determining the three-dimensional configuration of the components in all the grades (sizes) of the respective shoe style is also very time-consuming and requires a high degree of expertise and experience.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel method and apparatus for making shoe lasts having advantages in the above respects. Another object of the invention is to provide a novel method and apparatus which may be also used for making the graded components of the shoes.

According to the present invention, there is provided a method of making shoe lasts, comprising: digitizing a large number of sample points on the outer surface of a model last representing a particular shoe style to produce a model last digital file representing the three-dimensional surface contour of the respective model last; grading the model last digital file to produce graded last digital files representing different last sizes of the respective shoe style; and utilizing the graded last digital files to produce graded shoe lasts of the respective shoe style.

According to an important feature in the preferred embodiments of the invention described below, the method includes the further steps of digitizing a large number of sample points on the feather line of the model last to produce a feather line digital file representing the feather line of the respective model last; and utilizing the feather line digital file, together with the model last digital file, for producing the plurality of graded last digital files of the respective shoe style.

The described preferred embodiments also include the further step of digitizing a large number of sample points on preselected style-lines of the model last to produce a style-line digital file for the respective shoe style. Such a style-line digital file may be used, together with the model last digital file, for producing a plurality of graded component digital files representing different sizes and configurations of the components e.g., the flat leather blanks, used in manufacturing the respective shoe style.

The invention also provides apparatus for use in making shoe lasts, comprising: rotary drive means for rotating a model last representing a particular shoe style; digitizing means for digitizing a large number of sample points on the outer surface of the model last to produce a model last digital file representing the three-dimensional surface contour of the respective model last; and grading means for producing from the model last digital file a plurality of graded last digital files representing different lengths and widths of lasts of the respective shoe style.

In one preferred embodiment described below, the digitizing means comprises a tracer probe in the form of a rotary wheel; rotary drive means for rotating the model last about its longitudinal axis, constituting a first axis; a first encoder producing an electrical output representing the instantaneous angular position (e.g., ".theta.") of the model last about the first axis; a spring urging the tracer probe along a second axis in contact with the outer surface of the model last as the model last is rotated by the rotary drive means about the first axis; a second encoder producing an electrical output representing the instantaneous position (e.g., "X") of the tracer probe along the second axis; linear drive means for driving the tracer probe along a third axis parallel to the first axis; and a third encoder producing an electrical output representing the instantaneous linear position (e.g., "Z") of the tracer probe along the third axis.

In this described embodiment, the digitizing operation measures the instantaneous position (X, .theta., Z) of the tracer probe at each sample point to represent the "tool" path points (i.e., the center point of the tracer wheel) on the three-dimensional surface contour of the respective model last; and the grading operation converts the tool path points to "part" points on the surface of the model last, grades the part points to represent different lengths and widths of lasts of the respective shoe style, and then reconverts the graded part points to tool path points in the graded digital files.

In a second described embodiment, the digitizing means comprises an optical device directing an optical beam, such as a laser beam, against the outer surface of the model last as the model last is rotated about its longitudinal axis, and as the optical beam is advanced parallel to the longitudinal axis of the model last. In this described embodiment, the digitizing operation directly measures the part points on the surface of the model last; and the grading operation grades the part points to represent different lengths and widths of lasts of the respective shoe style, and then converts the graded part points to tool path points in the graded digital files.

As will be described more particularly below, the novel method and apparatus may be used for making graded shoe lasts, and also graded components of shoes, in a quick and efficient manner as compared to the present techniques. Moreover, the method and apparatus of the present invention permits various "holding" techniques to be conveniently applied in order to hold a particular dimension of the shoe last for more than one grade, or to provide a disproportionate change in one or more dimensions with respect to the other dimensions among different grades. Such techniques may be used to avoid distortions in the graded shoes, and also to minimize the initial tooling required to make the shoe components.

The method and apparatus may be embodied in new equipment specifically designed for making shoe lasts or components in accordance with the invention, or may be added to existing equipment, e.g., of the pantographic type, to retrofit such equipment for making graded shoe lasts in accordance with the present invention.

Further features and advantages of the invention will be apparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating one form of apparatus constructed in accordance with the present invention for making shoe lasts and/or shoe components;

FIG. 2 illustrates a typical model last representing a particular shoe style used for producing graded lasts for the different sizes of the respective shoe style;

FIG. 3 illustrates the digitizing means included in the apparatus of FIG. 1;

FIG. 4 is a three-dimensional view illustrating the three axes defining the sample points on the outer surface of the model last;

FIG. 5 is a block diagram illustrating the digitizer computer in the system of FIG. 1;

FIG. 6 is a flow diagram illustrating the man-machine interface (MMI) software in the digitizer computer of FIG. 1;

FIG. 7 is a flow diagram illustrating the operation of the digitizer computer of FIG. 1;

FIG. 8 is a flow diagram illustrating the man-machine interface (MMI) software in the grading computer of FIG. 1;

FIG. 9 is a flow diagram illustrating the operation of the grading computer in the system of FIG. 1;

FIGS. 10a and 10b are diagrams helpful in explaining the manner of determining the part points i.e., the points on the surface of the model last, from the measured tool path points;

FIG. 11a illustrates a model last and one graded last produced therefrom, including different part of such lasts, and also illustrates the manner of modifying the change in one of the dimensions (i.e., toe spring) in the produced graded last to avoid distortions;

FIGS. 11b and 11c are diagrams illustrating, in full lines, lasts which have been graded proportionately, and in broken lines the modifications of the graded lasts in order to apply other "holding" techniques for avoiding distortions for minimizing initial tooling costs;

FIG. 12 is a flow diagram illustrating the application of a "bottom holding" technique in producing a graded last;

FIG. 13 is a last diagram helpful in explaining the heel-height holding technique;

FIG. 14 is a flow diagram explaining the heel-height holding technique applied to the last illustrated in FIG. 13;

FIGS. 15a and 15b are diagrams helpful in explaining the manner of modifying the digital data identifying each sample point on the surface contour of the last according to the "holding" technique applied to the last;

FIG. 16a illustrates a last having a number of style-lines marked thereon to indicate the configurations of different components used in manufacturing the shoe corresponding to the last;

FIG. 16b is a flow diagram illustrating the manner of using the style-lines in FIG. 16a for producing the graded components used to manufacture the shoes of the graded lasts;

FIG. 17 illustrates an optical digitizer, namely a laser system, which may be used for the digitizer in the system of FIG. 1; and

FIG. 18 is a flow diagram illustrating the operation of the grading computer when using the laser digitizer of FIG. 17.

DESCRIPTION OF PREFERRED EMBODIMENTS

Overall System Illustrated in FIG. 1

FIG. 1 is a block diagram illustrating an overall system for making shoe lasts in accordance with the present invention. The system includes a digitizer, within the block generally designated 2, which digitizes a large number of sample points on the outer surface of a model last ML representing a particular shoe last style. This digital information is outputted to a digital computer 4 which produces a model last digital file 5 representing the three-dimensional surface contour of the respective model last.

FIG. 2 illustrates one form of model last ML representing a particular shoe style. Among its other components, the illustrated model last ML includes a last bottom LB, a last heel LH, and last sides LS. The juncture line of the last sides LS with the last bottom LB and last heel LH is called the feather line FL, and is an important element in the shoe style of the respective last. As also seen in FIG. 2, the last sides LS include a plurality of style-lines SL, which are important elements not only in the particular shoe style of the respective last, but also in the configuration of the components, e.g., leather blanks, used in making the shoe of the respective style.

Digitizer unit 2 illustrated in the system of FIG. 1 digitizes not only the sample points on the outer surface of the model last ML to produce the model last digital file 5, but also digitizes the feather line FL of the model last, which information is outputted to the digitizer computer 4 to produce a feather line digital file 6. Digitizer 2 also digitizes the style-lines SL of the model lasts ML, which information is also outputted to the digitizer computer 4 to produce a style-line digital file 7. Since the feather line file 6 and the style-line file 7 are substantially smaller than the model last file 5, files 6 and 7 may be integrated into a single joint file, and thereafter processed as a single file with the model last file 5. These files may be embodied in diskettes, cassette tapes, or in any other suitable form.

As further shown in FIG. 1, the digitizer file 5, feather line file 6, and style-line file 7, are inputted into a grading computer 8 which produces a plurality of graded last digital files. These may also be embodied in the form of diskettes or cassette tapes suitable for use in a CNC (computerized numerical control) last cutting machine, indicated at 10, which uses this information for cutting the plurality of graded lasts for each shoe style represented by the model last ML. The graded last files 9 may also be used in an existing last-cutting machine (e.g., of the known pantographic type) retrofitted, as indicated at 11, so as to receive the graded last files 9 and to use this information for cutting the graded lasts.

The grading computer 8 may also produce a plurality of graded component files 12 for the components, e.g., leather blanks, used for making the shoes in the various grades of the particular shoe style of the model last ML. The graded component files 12, also in the form of diskettes or cassette tapes for example, may be inputted into existing component cutting machines, indicated at 13, for cutting the graded components to be used for making the shoes.

The digitizer computer 4 includes a keyboard KB.sub.1 and a display DISP.sub.1 enabling operator control of the computer to produce the three files, 5, 6 and 7, as will be described more particularly below. Similarly, the grading computer 8 also includes a keyboard KB.sub.2 and a display DISP.sub.2 enabling operator control of the computer to produce the files 9 and 12, as will also be described more particularly below.

The Digitizer Unit 2

FIG. 1 illustrates in block diagram form the electrical system included in the digitizer unit 2; FIG. 3 illustrates the mechanical construction of the digitizer unit 2; and FIG. 4 illustrates the digital coordinates (X, .theta., Z) of each of the sample points on the outer surface of the model last which are measured by the digitizer unit 2 to produce the model last digital file 5 as well as the feather line file 6 and style-line file 7.

As shown in FIG. 1, digitizer unit 2 includes a rotary motor M.sub.74 for rotating the model last ML about its longitudinal axis, hereinafter referred to as the turning center line TCL, and an encoder E.sub..theta. producing an electrical output representing the instantaneous angular position (.theta.) of the model last ML about line TCL. The digitizer unit further includes a tracer probe TP urged by a spring 14 along a second axis (X-axis) into contact with the outer surface of the model last ML as the model last is rotated about its turning center line TCL, and an encloder E.sub.X producing an electrical output representing the instantaenous position of the tracer probe along the X-axis. Digitizer unit 2 further includes a motor M.sub.Z for driving the tracer probe TP along a third axis (the Z-axis), parallel to the turning center line TCL of the model last ML, and an encoder E.sub.Z producing an electrical output representing the instantaneous linear position of the tracer probe TP along the Z-axis.

As shown in FIGS. 4 and 4a, each point in space is defined, in each plane, by polar coordinates, namely by the dimension "X", being the instantaneous linear position of the center of the tracer probe TP along the X-axis, and the angle .theta., being the instantaneous angular position of the last about the turning center line TCL; and each plane is defined by the instantaneous linear position of the tracer probe TP along the Z-axis. The center points of the tracer probe thus represent the "tool" path points (points "T" in FIG. 10a). Since the diameter of the tracer probe TP is known, the position in space of the surface contact point on the outer contour of the last (referred to as the "part" points in FIG. 10a) can be easily determined.

Encoders E.sub.X, E.sub..theta. and E.sub.Z may be digital-type encoders of known construction which output a series of digital pulses representing their respective instantaneous values; alternatively, the encoders could be of the analog type, in which case the analog information outputted by them would be converted to digital form by an analog-to-digital converter, as also known. As described above, the digital information from the encoders E.sub.X, E.sub..theta. and E.sub.Z is inputted into the digitizer computer 4 for producing the respective digitizer file 5, feather line file 6, and style-line file 7, under the control of the operator via keyboard KB.sub.1 and display DISP.sub.1.

The mechanical construction of the digitizer unit 2 is more particularly illustrated in FIG. 3. The tracer probe TP is in the form of a wheel which is urged by loading spring 14 (a second one, not shown, being provided on the opposite side of the wheel) into contact with the outer surface of the model last ML. The model last is secured between a heel dog 16 and a tail stock 18, and is rotated by electrical servomotor M.sub..theta. about the longitudinal axis TCL. The tracer probe wheel TP, and its loading spring(s) 14, are carried by a carriage 20 movable along a pair of rails 22 parallel to the longitudinal axis TCL of the model last ML by means of a ball screw 24 rotated by the servomotor M.sub.Z. Thus, by operating motor M.sub..theta. to rotate the model last ML about its longitudinal axis TCL and by operating motor M.sub.Z to drive the tracer probe wheel TP along the Z-axis, parallel to the longitudinal axis TCL of the model last, the tracer probe wheel TP scans the complete outer surface of the model last.

During the scanning operation, the instantaneous position of the tracer probe TP on the outer surface of the model last ML, as measured by the respective encoders E.sub.X, E.sub..theta. and E.sub.Z, is periodically recorded. This data thus identifies the sample points on the outer surface of the model last representing the particular shoe style of the last. A large number of sample points, e.g., in the order of 15,000, is required for this purpose; for example, 90 sample points may be taken for each plane or slice, and 100-200 slices may be taken, depending on the model last. However, since the sample points are taken "on the fly" during the continuous rotation of the model last ML, the complete digitizing procedure may be done in only a few minutes, whereas automatic point-to-point sampling of the outer surface of the last would take many hours.

During this digitizing procedure, rotary motor M.sub..theta., which rotates last ML, is operated continuously. Servomotor M.sub.Z may also be operated continuously to move the tracer probe wheel TP along the Z-axis, in which case the scanning of the outer surface of last ML by the tracer probe TP would be in a spiral manner. Alternatively, servomotor M.sub.Z may be operated intermittently, following each rotation of the model last ML by the servomotor M.sub..theta., in which case the scanning of the outer surface of the model last by the tracer probe TP would be in a stepped manner.

Digitizer unit 2 illustrated in FIG. 3 further includes two limit switches LS.sub.1, LS.sub.2, at the opposite ends of the model last ML and engageable by elements carried by carriage 20. Switches LS.sub.1, LS.sub.2 limit the linear movement of the carriage along the Z-axis.

Carriage 20 further includes an optical sensor OS used for sensing the style-lines SL (FIG. 2) of the model last ML. For this purpose, the style-lines SL on the model last ML have a different optical characteristic from the remainder of the model last ML; for example, the model last could be of a light color, and the style-lines SL could be of a dark color.

Optical sensor OS may also be used for sensing the feather line FL of the model last ML. Preferably, however, the feather line FL is sensed by the tracer probe TP. For this purpose, the model last ML is of electrically insulating material except for the last bottom LB (FIG. 2), which is of electrically conductive material. Thus, the juncture line between the last bottom LB and the last sides LS, constituting the feather line FL of the last, is detectab