WO2004070315A1

WO2004070315A1 - Method and apparatus for determining the three-dimensional shape and dimensions of an object

Info

Publication number: WO2004070315A1
Application number: PCT/IL2004/000119
Authority: WO
Inventors: Noam Danenberg; Samuel Kosolapov
Original assignee: Fitracks Ltd.
Priority date: 2003-02-06
Filing date: 2004-02-05
Publication date: 2004-08-19
Also published as: IL154345A0

Abstract

The present invention provides a method and apparatus for determining the three-dimensional shape and dimensions of a human foot. The invention is based on projecting a plurality of parallel planes of laser light on the foot, receiving the reflected image of the intersection of the planes of light with the foot in a digital image capturing device, and processing the reflected images to reconstruct the three-dimensional surface of the foot.

Description

METHOD AND APPARATUS FOR DETERMINING THE THREE-

DIMENSIONAL SHAPE AND DIMENSIONS OF AN OBJECT

Field of the Invention

The present invention relates to the field of capturing information regarding

the surface shape of an object. Specifically the present invention provides a

method and apparatus for determining the three-dimensional shape and

dimensions of a human foot.

BACKGROUND of the Invention

The problem of obtaining accurate foot measurements has existed since man

first started to wear shoes. Until recently the majority of solutions have been two-dimensional, providing measurements of length and width only.

Representative of such solutions is that of Charles Brannock, disclosed in

U.S. Patent No. 1,725,334. Brannock's device, familiar to anyone who has

ever visited a shoe store, basically consists of two slides mounted on an

indexed base plate to determine the length and width of the foot.

Since Brannock's day the technology has improved, providing pressure

sensors and light sensitive sensors of various types to measure the length and the width of the foot. In U.S. 5,659,393 is presented a system that improves somewhat on the existing foot measurement systems. The system

disclosed in this patent utilizes a combination of a pressure pad assembly

for each foot surrounded by a number of infrared LEDs and phototransistors

located around the perimeter of each pressure pad. This system gives

information about height at selected locations along the perimeter of the

foot in addition to the traditional length and width measurements. However

no known foot measurement system supplies a complete digital three-

dimensional image of a human foot. Without such an image there is a

limitation to the quality of the fit of the shoe that can be determined for the

measured foot.

It is a purpose of the present invention to provide a method for providing a

complete digital three-dimensional image of a human foot

It is another purpose of the present invention to provide a method for

measuring the dimensions of the human foot.

It is yet another purpose of the present invention to provide an apparatus

for performing the measurements that are needed to provide a complete

digital three-dimensional image of a human foot.

Further purposes . and advantages of this invention will appear as the

description proceeds. Summarv of the Invention

The present invention provides a method and apparatus for determining the

three-dimensional shape and dimensions of a human foot. The invention is

based on projecting a plurality of parallel planes of laser light on the foot,

receiving the reflected image of the intersection of the planes of light with

the foot in a digital image capturing device, and processing the reflected images to reconstruct the three-dimensional surface of the foot. The method

of the invention, in one of its most preferred embodiments, does not require

precise alignment of mechanical or optical elements and the apparatus of

the invention does not contain any moving parts. It is however possible to

replace multiple static lasers for each slice with combination of motor and

single laser, producing the same effect of multiple lines on different

elevation.

In a first aspect, the present invention is directed towards providing an

apparatus for determining the three-dimensional shape and dimensions of

an object. The apparatus of the invention comprises:

a) a housing comprising a measuring surface on which the object

is placed;

b) computing means; c) input/output devices for the computing means; d) two or more towers, each comprising a vertically elongated

support structure, wherein each of the towers contains a

plurality of light sources;

e) for each of the light sources, optical beam shaping means;

f) two or more lenticular arrays of cylindrical lenses;

g) two or more optical light gathering means;

h) two or more digital image capturing devices;

i) means for independently activating each of the light sources

according to a predetermined sequence; and

j) optionally, an electronic pressure sensitive pad;

The software supplied with the computing means makes use of a pre¬

determined software calibration table stored in its memory as the basis of

instructions allowing the computing means to compensate for shifts and

rotations of the object relative to a coordinate system associated with the

housing. Thus it is unnecessary to position the object in a fixed and pre¬

determined manner within said housing. In the preferred embodiment of the

invention, the number of towers is four and the number of light sources is 32

to 40. In a preferred embodiment the light sources are low powered lasers.

In a second aspect, the present invention is directed towards providing a

method for using the apparatus of claim 1 for determining the three- dimensional shape and dimensions of an object. The method of the invention

comprises:

a) independently projecting parallel planes of light from a

plurality of light sources on the object;

b) receiving the reflected images of the intersections of the planes

of light with the object in a digital image capturing device; and

c) processing the reflected images to reconstruct the three-

dimensional surface of the object.

The surface of the object being measured can have any color or texture that

does not substantially absorb or scatter the light emitted by the light

sources. Typical of the type of object whose three-dimensional shape and

dimensions can be determined using the apparatus and method of the

invention is a human foot.

The method for using the apparatus of the invention for determining the

three-dimensional shape and dimensions of an object comprises two steps:

a) determining a software calibration table;

b) using said software calibration table to determine the surface

measurements and shape of said object.

The software calibration table is constructed by performing the following steps: a) activating the light source . that will produces laser line zi on

the surface of a calibration object, wherein laser line zi is the

intersection of the planar beam emitted from the light source

with the surface;

b) placing the calibration object at known position xi on the

measurement surface;

c) using a digital image capturing device to record the image

comprising the laser line Zi superimposed upon the calibration

lines marked on the sides of the calibration object;

d) assigning for each Xi,yi,zι of the space defined by the calibration

object and the corresponding points x,y on the focal plane of the

digital image capturing devices a calibration point in the

software calibration table;

e) repeating steps (b) to (d) for all i positions on the

measurement surface; and

f) repeating steps (a) to (e) for each light source in all of the

towers in the apparatus.

Once the software caHbration table has been obtained it is used to

determine the surface measurements and shape of an unknown object by

carrying out the following steps:

a) . illuminating the object with the beam of light from first

light source of the first tower of the apparatus; b) capturing, with the image capturing device associated

with the first tower, the image of the intersection of the

light beam with the object;

c) repeating steps (a) and (b) for all of the light sources of

the first tower;

d) repeating steps (a), (b), and (c) for all the towers in the

apparatus;

e) determining, by measuring the peak intensity of the

reflected light in the images, the relative position of the

intersections of the light beams with the object for each

of the z planes for each of the towers;

f) using the images captured by the digital image

capturing devices to calculate the Xi,Yι,Zι values for

points on all of the lines of intersections of the light beams with the object by using linear interpolation

between the closest calibration points (preferably four) in the previously determined software calibration table;

and

g) determining the surface measurements and shape of the

object by interpolation between the points calculated in

step (f). In another embodiment of the apparatus of the invention, the plurality of

light sources contained in each of the towers is replaced by a single light

source coupled with light directing means. The light directing means can

include a motor or mirrors and/or other optical elements.

All the above and other characteristics and advantages of the invention will

be further understood through the following illustrative and non-limitative

description of preferred embodiments thereof, with reference to the

appended drawings.

Brief Description of the Drawings

Fig. 1 schematically shows a general view of the apparatus of the

invention;

Fig. 2A schematically shows the principle of the method of the

invention;

Fig. 2B is a copy of a photograph showing the intersection of a single

laser beam with a test object;

Fig. 3A schematically shows the optical system used to generate the

planar shaped beam of light of Fig. 2;

Figs. 3B, 3C, and 3D schematically show the beam profile in a plane

perpendicular to the optical axis of the optical system of Fig. 3A at

selected positions along the optic axis; Fig. 3E schematically shows a cross section of a portion of lenticular

lens array of Fig. 3A;

Fig. 4A schematically shows the case of three parallel planes of

illuminating light;

Fig. 4B schematically shows a tower comprised of five light sources;

Figs. 5A and 5B schematically show the method of calibrating the

apparatus of the invention;

Figs. 6 to 8 are screenshots showing some of the internal processing

results for a single foot;

Fig. 9 is a screenshot showing three-dimensional maps of the feet;

and

Fig. 10 is a screenshot showing a pressure map made using a

pressure pad.

Detailed Description of Preferred Embodiments

Fig. 1 schematically shows a general view of the apparatus of the invention.

The components of measuring apparatus 1 are arranged inside a housing 2.

As can be seen from the figure, housing 2 is comprised of a floor 3, back wall

4, and two side walls 5, all of these defining an internal space (referred to

hereinbelow as the "measurement space") into which the item (foot) to be

measured is inserted. Floor 3 is also referred to hereinbelow as "the

measurement surface". On the interior sides of each of the two side walls 5

are a plurality of slits 6 (only three illustrative slits are shown in the figure, but their number is not intended to be limited other than by design

considerations) and a window 7, the purpose of which is to allow passage of

light beams to and from optical elements that are positioned in the at least

partially hollow interior of wall 5. The structure and function of these

optical elements will be described hereinbelow. In a preferred embodiment

of the invention, an electronic pressure sensitive pad 8 is provided on, or

built into, the floor 3 of the apparatus.

The apparatus of the invention also includes a microprocessor, personal

computer, or similar device and appropriate input and output devices to

store the data, perform the necessary computations to calibrate the device,

and calculate and display the three-dimensional dimensions and shape of

the foot. All of these devices are conventional and therefore neither

described in the description herein nor shown in the accompanying figures,

for the sake of brevity.

Fig. 2A schematically shows the principle of the method of the invention.

Optical system 20 (to be described hereinbelow with reference to Figs. 3A to

3E) is designed to project a planar shaped beam of light through one of slits

6. The beam of fight strikes an object, in this case foot 22, which is located in

its path of propagation. The intersection of the planar beam of light and the

three dimensional object is the curved line 23 which appears on the surface

of the object. The light reflected from the object is gathered by an appropriate optical arrangement 24 and focused onto the focal plane of a

digital image capturing device 25, for example a CCD device.

Fig. 2B is a copy of a photograph showing the intersection of a single laser

beam with a test object.

Fig. 3A schematically shows the optical system 20 used to generate the

planar shaped beam of light 21. Numeral 31 designates a Hght source which

can be any source of light having a high enough intensity such that light

reflected from the object can be detected by the image capturing device. In

the preferred embodiment of the invention, the light source is a low power

laser operating in the visible range. A typical commercially available laser

that is suitable for use in the invention is a Model LM8.5-630-3 laser module

produced by Olympic Trade Ltd. of Hong Kong. This laser has an output of

about 3mW at 650nm.

The light source is followed by optical element (or group of elements) 32 the

function of which is to convert the output profile of the laser beam from a

generally circular shape to a collimated beam having an essentiaHy

elongated oval shape. The beam is orientated such that the long axis of the

oval is horizontal, i.e. parallel to the floor 3 (Fig. 1) of the measuring

apparatus 1. When this beam of Hght passes through cyhndrical lens 33, it

is magnified in the direction of its horizontal axis and its magnification in the vertical direction" is unchanged. Cylindrical lens 33 is one of many

identical lenses that comprise lenticular lens array 34. The optical

properties, such as focal length, radius, thickness, and spacing of the

paraHel lenses in array 34 can be easily determined by the skilled person

such that the elongated image of the shaped laser beam that is produced by

several of the individual lenses will overlap with that of its neighbors

resulting in planar output beam 21.

Figs. 3B, 3C, and 3D schematicaUy show the beam profile in a plane

perpendicular to the optical axis of system 20 at positions B, C, and D

respectively. As described hereinabove, the profile shown in Fig. 3D is that

of an individual lens in the lenticular array 34 and beam 21 is comprised of

a number of overlapping profiles from other lenses in the array.

Fig. 3E schematically shows a cross section of a portion of lenticular lens

array 34 in a plane perpendicular to the longitudinal axis of the cylindrical

lenses. In the figure, the radius of the lenses is denoted by r, the distance

between adjacent lenses by d, and the sag of the lens by s.

All of the optical principles and elements needed to construct the measuring

apparatus of the invention are weH known in the art and will therefore not

be discussed in further detail herein. AdditionaUy, it can be understood that

the skilled person, having understood the concept of the invention from the description provided herein, will be able to devise many different suitable

optical arrangements.

As shown in Fig. 2, and as will be described hereinbelow, the image of

curved line 23 that is captured by device 25 is used to determine the

distance from any point on line 23. According to the method of the invention,

a multitude of parallel lines 23i are projected onto the foot at different

heights zi above the floor. From the distance measurements for many points

on each of the multitude of fines the three dimensional shape and

dimensions of the foot 22 can be determined.

Fig. 4A schematicaUy shows the case (simplified for the sake of clarity of

illustration) of three parallel planes of illuminating light. In order to get an

accurate three-dimensional representation on an average adult foot it has

been found that projections at eight to ten different heights are sufficient In

order to produce this set of parallel beams of light, a motor-driven

mechanical elevation system could be employed to change the height of

optical system 20 in a controlled and predetermined fashion. However, in

the preferred embodiment of the present invention, it is desired to avoid the

complications and possible source of operational failures inherent in

mechanical systems and moving parts. Therefore in the preferred

embodiments of the invention, a plurafity of optical systems 20, equal to the

required number of parallel beams of light, are provided. The plurality of light sources and accompanying beam shaping optics are stacked and

supported in vertically elongated support structure. This support structure,

including the light sources and shaping optics, is referred to in this

specification as a tower.

The light sources and accompanying optical elements are vertically spaced a

fixed distance (not necessarily equidistant) apart and either individual

lenticular lens arrays 34 or, preferably, a single array having a height at

least equal to that of the tower is supported in the appropriate position. In

order to obtain a complete image of the foot, at least two towers, one on each

side are provided. In Fig. 4B is schematically shown a tower 40 comprised of

five Hght sources 31i. In order to allow for vertical spacing of the parallel

planar light beams that is less than the vertical physical height of the

individual Hght sources they can be staggered as shown in Fig. 4B. Design of the tower and arrangement of the optics can be accomplished by the

experienced person and therefore will not be discussed in detail herein for

reasons of brevity.

The microprocessor or PC that is part of the system of the invention causes one light source at a time to be activated and the image of the light reflected

from the foot to be recorded. When all of the light sources have been

activated, the entirety of the collected data is analyzed as wiH be described hereinbelow and the three dimensional shape and dimensions of the foot are

determined.

In order to calculate the location of any given point on the surface of the

foot, the apparatus must be calibrated. The calibration is accomplished with

the aid of a caHbration object such as those shown in Figs. 5A and 5B. In

Fig. 5A is shown a caHbration object having vertical reference lines on its

surface. The caHbration object is placed at the origin of an x,y coordinate

system and iHuminated by a plane of light at height ZL The image of the

intersection of the laser beam with the calibration object is recorded on the

CCD. The caHbration object is now moved to a different position on the floor

of the casing with a different value of i and the image is again recorded.

The result of repeating these steps is a calibration table in the memory of

the computer for each value of ZL This table relates specific points (x,y), i.e.

specific pixel locations, on the two dimensional grid of the CCD with a

unique coordinate (xi,yi,,zi) in the measurement space. From the known

coordinates of a large set of points on the surface of the foot its three-

dimensional shape can be calculated.

In a preferred embodiment of the housing of the apparatus of the invention,

sockets, into which the calibration object fits, are provided in the floor in

order to guarantee accurate calibration. To carry out effective calibration,

the calibration object is positioned to within an accuracy of less than 1 mm. Using the caHbration table described hereinabove, the three-dimensional

coordinates of any point on the surface of the foot can be determined from

the captured images of the reflected laser light. If the distance to a point on

the image that does not exactly correspond to those in the caHbration curve

is to be measured then standard interpolation techniques are employed to

determine its coordinates. Calibration is carried out when setting up the

apparatus, whenever it is moved, and either periodically, e.g. once per

month, or whenever special diagnostic software supplied with the apparatus

detects a suspected problem with the measurements. All of the

computational methods and the methods of producing appropriate software

necessary to perform the caHbration, calculate the distances, and calculate

and display the three dimensional shape of the foot are well known to the

skilled person and therefore are not described herein.

Fig. 5B is shown a calibration object having both horizontal and vertical

reference lines on its surface. Using this calibration object the Zi coordinates

can be determined together with _x and i, thus any errors that might be

caused by misafignment of the optics in any of the levels of the tower

supporting the Hght sources can be eliminated.

In another preferred embodiment of the invention, a pressure sensitive pad

(numeral 8 in Fig. 1) is included to provide additional information about the shape and dimensions of the bottom of the foot. Examples of commercially

available pressure sensitive pads are those having the name "Twin PeH"

made in France or "Novell" manufactured in Germany.

As will be apparent to the skilled person, the calibration and measurements

are carried out for each of the Hght source -containing towers and image

capturing devices, in order to get a complete view of the foot. Further the

apparatus and method of the invention can be used to determine the three-

dimensional shape of any object that is placed in the internal space of the

measuring apparatus. Since the basis of the invention is the measurement

of the light reflected from the object, the only condition on the surface of the

object is that it be capable of reflecting a substantial portion of the light that

is incident upon it. In other words, the surface of the object can have any

color or texture that does not substantially absorb or scatter the light

emitted by the light sources. Additionally, more than two of the light source-

containing towers and associated image capturing devices may be provided

if necessary, to obtain images from every portion of the surface of the object

being measured and in the preferred embodiment four towers are used.

Measuring the three-dimensional shape and dimensions of an object is

carried out by following the steps outlined in the foHowing two algorithms:

I. Algorithm for caHbration: a. activate the light source that produces laser line zi on the

surface of the calibration object;

b. place the calibration object at known position Xi on the

measurement surface;

c. record the image of the laser fine zi superimposed upon the

calibration fines marked on the calibration object with the

corresponding digital image capturing device;

d. assign for each Xi,yi,zi of the space defined by the calibration

object and the corresponding points x,y on the focal plane of the

digital image capturing devices a calibration point in the

software calibration table;

e. repeat steps (b) to (d) for all xi positions on the measurement

surface; and f. repeating steps (a) to (e) for each light source in all of the

towers in the apparatus.

Algorithm for measuring three-dimensional shape and dimensions of an object:

a. iHuminate the object with the beam of Hght from first light

source of the first tower;

b. capture, with the image capturing device associated with the

first tower, the image of the intersection of the light beam with

the object; c. repeat steps (a) and (b) for all light sources of the first tower;

d. repeat steps (a),(b), and (c) for all the towers;

e. determine, by measuring the peak intensity of the reflected

light in the images, the relative position of the intersections of

the light beams with the object for each of the z planes for each

of the towers;

f. calculate the Xi,Yi,Zi values for points on all of the fines of

intersections of the light beams with the object by using linear

interpolation between the closest calibration points (preferably

four) in the software calibration table; and

g. determining the surface measurements and shape by

interpolation between the points calculated in step (f).

It will be appreciated by skilled persons that, in order to determine the three dimensional shape and dimensions of an object using the apparatus of

the invention, it is unnecessary to position the object in a fixed and pre¬

determined manner relative to the components of the apparatus. This is

possible because the software supplied with the computing means of the

apparatus, and used to perform the computational steps outlined in the

algorithms described hereinabove, is capable of using the pre-determined

software calibration table stored in the computing means memory as the

basis of instructions allowing the computing means to compensate for shifts and rotations of the object relative to a coordinate system associated with

the housing.

Example

The following is a non-limiting example intended to demonstrate the

invention. In this example, various dimensions of the feet of an adult male

were measured using the apparatus and method of the invention as

described hereinabove. The results of the measurements are shown

graphically in Figs. 6 to 10 and are summarized in the table hereinbelow.

Figs. 6 to 8 are screenshots showing some of the internal processing results

for a single foot. Fig. 9 is a screenshot showing three-dimensional maps of

the feet. The skilled person will reafize that the data can be manipulated,

using weH-known techniques, to enable the acquisition of a three-

dimensional map having virtuaHy any desired viewing angle.

The following table gives the measurements computed from the three-

dimensional data for both feet. Shown in the table are a set of basic

measurements only. The software of the apparatus is able to make and

display an essentiaHy unlimited number of measurements to describe any

conceivable feature of the three-dimensional object. The position of the

maximum width of each foot is measured from the heel of that foot. Measurements taken manuaUy are included in the table for comparison. All

measurements in the table are in mm.

Fig. 10 is a screenshot showing a pressure map made using pressure pad 8,

shown in Fig. 1. The use of the pressure pad allows additional information

about the feet, i.e. arch and insole, to be determined.

Although embodiments of the invention have been described by way of

illustration, it will be understood that the invention may be carried out with

many variations, modifications, and adaptations, without departing from its

spirit or exceeding the scope of the claims.

Claims

1. An apparatus for determining the three-dimensional shape and

dimensions of an object comprising:

a) a housing comprising a measuring surface on which said object

is placed;

b) computing means;

c) input/output devices for said computing means;

d) two or more towers, each comprising a vertically elongated

support structure, wherein each of said towers contains a

plurality of light sources;

e) for each of said light sources, optical beam shaping means;

f) two or more lenticular arrays of cyfindrical lenses;

g) two or more optical light gathering means;

h) two or more digital image capturing devices;

i) means for independently activating each of said light sources

according to a predetermined sequence; and

j) optionally, an electronic pressure sensitive pad;

wherein, software supplied with said computing means makes use of a pre¬

determined software calibration table stored in the memory of said

computing means as the basis of instructions allowing said computing

means to compensate for shifts and rotations of said object relative to a

coordinate system associated with said housing, thereby making it unnecessary to position said object in a fixed and pre-determined manner

within said housing.

2. Apparatus according to claim 1, wherein the Hght sources are low

powered lasers.

3. An apparatus according to claim 1, wherein the number of towers is four

and the number of light sources is 32 to 40.

4. A method for using the apparatus of claim 1 for determining the three-

dimensional shape and dimensions of an object comprising:

a) independently projecting parallel planes of light from a

plurafity of Hght sources on said object;

b) receiving the reflected images of the intersections of said planes of light with said object in a digital image capturing

device; and c) processing said reflected images to reconstruct said three-

dimensional surface of said object.

5. A method according to claim 4, wherein the surface of the object can have

any color or texture that does not substantiaHy absorb or scatter the

light emitted by the light sources.

6. A method according to claim 4, wherein the object is a human foot.

7. A method for using the apparatus of claim 1 for determining the three-

dimensional shape and dimensions of an object comprising:

a) determining a software calibration table;

b) using said software calibration table to determine the surface

measurements and shape of said object.

8. A method according to claim 7, wherein the software calibration table is

constructed by performing the foHowing steps:

a. activating the light source that will produces laser fine zi on

the surface of a caHbration object, wherein laser line zi is the

intersection of the planar beam emitted from the light source

with said surface;

b. placing said calibration object at known position Xi on the

measurement surface;

c. using a digital image capturing device to record the image

comprising said laser line Zi superimposed upon the calibration

fines marked on the sides of said calibration object;

d. assigning for each Xi,yi,Zi of the space defined by said calibration

object and the corresponding points x,y on the focal plane of the

digital image capturing devices a calibration point in the

software calibration table; e. repeating steps (b) to (d) for all i positions on said

measurement surface; and

f. repeating steps (a) to (e) for each light source in all of the

towers in the apparatus.

9. A method according to claim 7, wherein the software calibration table is

used to determine the surface measurements and shape of the object by

carrying out the foHowing steps:

a. iHuminating the object with the beam of light from first

light source of the first tower of the apparatus;

b. capturing, with the image capturing device associated

with said first tower, the image of the intersection of

said light beam with said object;

c. repeating steps (a) and (b) for all of the light sources of

said first tower; d. repeating steps (a), (b), and (c) for all the towers in the

apparatus; e. determining, by measuring the peak intensity of the

reflected light in the images, the relative position of the

intersections of the Hght beams with the object for each

of the z planes for each of the towers; f. using the images captured by said digital image

capturing devices to calculate the Xi,Yi,Zi values for points on aU of the lines of intersections of said Hght

beams with said object by using linear interpolation

between the closest calibration points (preferably four)

in the previously determined software calibration table;

and

g. determining the surface measurements and shape of

said object by interpolation between said points

calculated in step (f).

10. An apparatus according to claim 1, wherein the plurafity of light sources

contained in each of the towers is replaced by a single light source

coupled with light directing means.

11. An apparatus according to claim 10, wherein the light directing means

includes a motor.

12. An apparatus according to claim 10, wherein the light directing means

includes mirrors and/or other optical elements.