WO2003058162A1

WO2003058162A1 - A scanner system and a method for determining the surface coordinates of a three-dimensional object

Info

Publication number: WO2003058162A1
Application number: PCT/SE2003/000017
Authority: WO
Inventors: Anders Reyier
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-01-10
Filing date: 2003-01-10
Publication date: 2003-07-17
Anticipated expiration: 2004-07-10
Also published as: SE524582C2; SE0200069D0; AU2003203203A1; SE0200069L

Abstract

A scanner system arranged for determining coordinates of the surface of a three-dimensional object (1). The scanner system comprises a lighting unit (2) arranged so that it simultaneously generates a plurality of visible lines (3a-3c) intended for being reflected by different parts of the object, a sensor (5) arranged for detecting the reflected lines (6a-6c), and a calculating unit (7) adapted for calculating the coordinates of the surface in dependence of the detected lines. A method for determining the coordinates of a surface of a three-dimensional object, comprising simultaneously generating a plurality of lines of visible light intended for illuminating different parts of the object, reflecting the lines by the object, detecting the lines reflected by the object, and calculating the coordinates for the surface in dependence of the detected lines.

Description

A SCANNER SYSTEM AND A METHOD FOR DETERMINING THE SURFACE COORDINATES OF A THREE- DIMENSIONAL OBJECT

FIELD OF THE INVENTION

The present invention relates to a scanner system arranged for determining coordinates of the surface of a three-dimensional object, wherein the scanner system comprises a lighting unit arranged for generating a line of visible light intended to be re- fleeted by the object, a sensor arranged for detecting the line reflected from the object, and a calculating unit adapted for calculation of the coordinates in dependence of the detected line.

Further, the invention relates to a method for determining the coordinates of the surface of a three-dimensional object.

A scanner system is usually called a scanner. There are many applications, in which there is a need for determining the coordinates of the surface of an object surface. An example of such an application is a tooth mold, which is manufactured first by means of a scanner reading the coordinates for the surface of a casting of the tooth. Thereafter, the tooth mold is manufactured by means of a milling machine connected to the scanner, wherein the milling machine manufactures the tooth mold in depend- ence of the read coordinates of the surface of the casting.

A scanner system or a method according to the invention is not limited to any specific application and may be used for determining the coordinates of the surface of many different types of three-dimensional objects. PRIOR ART

A scanner station connected to a milling machine is disclosed in the European Patent Application No. EP 1 036 515 A2. The scanner is arranged such that it can read the coordinates of the surface of a foot and the milling machine is arranged such that it manufactures an inner sole of a shoe based on the read coordinates from the foot. The scanner station comprises a first laser unit arranged such that it moves along the underside of the foot. The laser unit emits a laser line, which is reflected by the foot and a sensor detects the reflected laser line. By measuring where on the sensor the reflected line is detected , the coordinates of the surface of the foot are calculated. Meanwhile, the laser unit moves along the foot the laser line is moved and the entire underside of the foot can be measured.

The scanner station also comprises a second and a third laser unit, which are arranged for measuring the surface of one side each of the foot. The second and the third laser units are ar- ranged in the same way as the first one and are moveable along the entire foot to make measure of the full length of the foot possible. All together, the three laser units are able to measure three sides of the foot. Disadvantages with the scanner station described above are that it is slow, heavy, lumbering and bulky. In certain applications, the scanner has to be transported between different places. Then, it is advantageous if the scanner station is small and easy to carry.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a scanner system, which is fast, inexpensive, light, and not bulky.

This object is achieved by the scanner system mentioned in the preamble, which is characterized in that the lighting unit is arranged such that it simultaneously generates a plurality of visi- ble lines intended for being reflected by different parts of the object, that the sensor is arranged for detecting the reflecting lines, and that the calculating unit is adapted for calculating the coordinates of the surface in dependence of the detected lines.

By simultaneously generating a plurality of lines, which are reflected by different parts of the object, the measurement of the different parts of the object can be made simultaneously and thus the measuring becomes fast. Thanks to the fact that sev- eral parts of the objects are measured simultaneously, the distance the lighting unit has to be moved along the object to be able to measure the whole object is getting shorter. Since the distance that the lighting unit has to be moved is getting shorter, the entire scanner system can be made shorter and thereby a small and compact system is obtained. Accordingly, the scanner system becomes robust, stable, and its calibration can be maintained after it has been transported.

According to a preferred embodiment of the invention, the scan- ner system is arranged such that the generated lines illuminate the object with essentially parallel lines. Accordingly, the measuring of the object is simplified.

According to a preferred embodiment of the invention, the light- ing unit is arranged for simultaneously generating at least three visible lines intended for being reflected by different parts of the object. The more parts of the object that can be measured simultaneously, the faster the method will become, and the distance that the lighting unit has to be moved during the measur- ing will become shorter. The number of necessary lines depends mainly on the application, but for achieving an essential decrease of the measuring time and the size of the system, the number of lines should be at least three.

According to a further embodiment of the invention, the sensor and the lighting unit are arranged so that the angle between the measuring direction of the sensor and the lighting unit is between 20° and 50°. Such an angle between the sensor and the lighting unit will provide an optimal measuring accuracy in relation to the geometry of the object. Which angle is later chosen within the interval depends on the geometry of the object.

According to a further embodiment of the invention, the lighting unit and the sensor are mounted on a carrier unit, wherein the carrier unit on one hand is arranged moveable in one direction along the object and on the other hand arranged rotateable in relation to the object. The carrier unit is advantageously arranged moveable in a direction along the longitudinal axis of the object and the carrier unit is arranged rotateable about an axis which is essentially parallel to the longitudinal axis of the object. Instead of arranging a plurality of lighting units, which measure one side each of the object, a lighting unit is arranged which is rotateable in relation to the object. Thus, the different sides can be measured with one and the same lighting unit, which just rotates to a new position before it measures the next side of the object. From an economical point of view it is advantageous to need only one lighting unit and further, the scanner system can be made even smaller and more compact.

According to another embodiment of the invention, the carrier unit is arranged adjustable in at least two predefined angular positions corresponding to the position of two sides of the object. It is beneficial if the predefined angular positions are at least three. Since the carrier unit is arranged adjustable in a number of predefined angular positions corresponding to the po- sitions of the object, it is possible to change fast between different sides of the object and the change can also be made automatically.

According to a further embodiment of the invention, it comprises a reflecting member arranged for reflecting at least the main part of the lines generated by the lighting unit in a direction to- wards the object. Preferably, the reflecting member is mounted on the moveable carrier unit. By reflecting the lines before they illuminate the object, the distance between the object and the lighting unit can be made shorter, which means that the scanner system can be made even smaller and more compact.

According to a further embodiment of the invention, the scanner system comprises a reflecting device arranged for reflecting at least one of the lines reflected by the object in a direction to- wards the sensor. It is advantageous if the reflecting device is arranged for reflecting the lines reflected from the short side of the object in a direction towards the sensor. Preferably, the reflecting device is arranged fixedly in relation to the object. Such an arrangement makes it possible to simultaneously measure a side of the object which is turned towards the sensor and another side of the of the object that is turned away from the sensor.

According to a further embodiment of the invention, the scanner system comprises a calibration means adapted for calibrating each line separately in dependence of a number of calibration tables. By calibrating each laser line separately by means of calibration tables especially produced for each individual laser line, an optimal calibration is achieved, which achieves an im- proved accuracy of the determination of the coordinates.

Another object of the invention is to provide a method for determining coordinates of the surface of a three-dimensional object, which method is fast and simple to use. This object is achieved with a method comprising simultaneously generating a plurality of lines of visible light intended for illuminating different parts of the object, reflecting the lines by the object, detecting the lines reflected by the object, and calculating the coordinates for the surface in dependence of the detected lines. BRI EF DESCRIPTION OF THE DRAWINGS

The invention will now be explained by the description of different embodiment examples and with reference to the appended figures.

Fig. 1 shows a scanner system according to an embodiment of the invention.

Fig. 2 shows a number of lines of visible light as the sensor detects them.

DESCRIPTION OF EMBODI MENTS

Figure 1 shows a scanner system arranged for determining a plurality of coordinates of the surface of a three-dimensional object 1 . The scanner system comprises a lighting unit 2 arranged for simultaneously generating a plurality of lines 3a-3c of visible light, which are intended for being reflected by different parts of the object, a sensor 5 arranged for detecting the visible lines 6a-6c reflected from the object 1 , and a calculating unit 7 adapted for calculating the coordinates of the surface in dependence of the detected lines. In this embodiment the lighting unit 2 is a laser, for example a diode laser, and is from now on de- noted the laser unit 2. The lines generated by the laser unit 2 are from now on denoted laser lines.

The laser lines are emitted in different directions towards a reflecting member, in form of a first mirror 9, and are reflected by the first mirror 9 in a direction towards the object 1. The laser unit 2 and the first mirror 9 are adjusted in relation to each other and the object so that the laser lines, reflected via the mirror 9, illuminate different parts of the object. The laser unit 2 is arranged so that the object is illuminated by essentially parallel lines and with essentially the same distance between the lines. The number of emitted laser lines is at least three and prefera- bly at least ten. The angle between the emitted laser lines, and the positioning of the laser unit 2 and the mirror 9 in relation to the object shall be such that each of the laser lines hit a different part of the object. If the same object is to be measured with a larger number of laser lines, the distance between the laser lines has to be reduced.

The laser unit 2, the sensor 5, and the first mirror 9 are mounted on a moveable carrier unit 10. The carrier unit 10 is arranged moveable in a direction x along a side of the object. The scanner system comprises a motor unit 12 arranged for linearly moving the carrier unit 10. If the object, whose surfaces the canner system is intended to read, has a length that essentially exceeds the width of the object, the carrier unit is arranged move- able in a direction along the length axis of the object. The distance that the carrier unit 10 has to move in relation to the object to be able to read the entire object, corresponds to the distance between two neighboring laser lines. Accordingly, the distance that the carrier unit has to be moved is shorter when the number of laser lines increases.

If the carrier unit is moved a distance that is longer than the distance between the laser lines, the measurements will overlap each other. In this embodiment example, it is preferred that the measurements do not overlap each other. Each laser line is intended for reading a smaller part of a larger continuous part of the surface of the object and together the laser lines read the entire continuous part of the object. Suitably, this large continuous surface is one side of the object and the smaller surface parts are a number of sequential parts, in the longitudinal direction, of the side.

Simultaneously, as the laser lines are moved along the object, the curvature of the reflected lines are read by means of the sensor 5. Advantageously, the sensor is a CCD sensor (Charge

Coupled Device). The positions of the lines on the sensor are a measurement of the distance to the object. The sensor and the laser unit ought to be arranged such that the angle between the measuring direction of the sensor and the longitudinal axis of the laser unit is between 20° and 50°. The exact value of the angle is determined in dependence on the desired accuracy and the geometry of the object. In this embodiment example, the angle between the sensor 5 and the laser unit 2 is about 45°.

During the measuring, the carrier unit 10 is moved along one side of the object. More sides of the object can be measured with the same equipment by rotating the carrier unit, with the laser unit, and the sensor such that the laser lines illuminate the other sides. The carrier unit 10 in figure 1 is mounted on a rotateable axis 14. The rotateable axis 14 is arranged essentially parallel to the longitudinal axis of the object. The carrier unit is arranged rotateable between a plurality of positions corresponding to the positions of at least some of the sides of the object. If the object, for example, has three long sides and one short side to be read, the carrier unit 10 and the rotateable axis 14 are ar- ranged such that the carrier unit is adjustable in at least three predefined angular positions corresponding to the position of the three long sides of the object. Thereby, it is possible to quickly and subsequently measure all three long sides. Between the measuring of two sides, the carrier unit is rotated so that the next side can be measured and during the measuring, the carrier unit is moved linearly along the side.

To be able to simultaneously measure a further side of the object, the first mirror 9 is arranged such that at least some of the laser lines, for example the laser line 3a, is reflected in a direction towards a first side 1 a of the object and at least some of the laser lines, for example the laser lines 3b, 3c, are reflected in a direction towards a second side 1 b of the object. The side 1 b is neighboring the side 1 a. The main part of the side 1 b faces the sensor 5 at the same time as the main part of the side 1 a is turned away from the sensor. Those laser lines 6c, which are reflected by the part of the object that faces the sensor, will directly hit the sensor 5. For the purpose of controlling the laser lines 6a, 6b that are reflected by the part of the object that is turned away from the sensor 5, in a direction towards the sen- sor, a reflecting device, in the form of a mirror 16, is arranged in the vicinity of the first side 1 a of the object. The mirror 16 is fixedly positioned in relation to the object, i.e. it is not arranged on the moveable carrier unit. The mirror 16 is arranged such that it receives laser lines 3a, which have been reflected by the first side 1 a of the object and laser lines 3b, which have been reflected by the side 1 b in a direction away from the sensor 5 and reflects the laser lines 6a, 6b that have been reflected by the object in a direction towards the sensor 5.

Figure 2 shows an example of how it looks like when the laser lines hit the sensor after having been reflected by the object. In figure 2, ten laser lines are shown. The sensor detects the position in the y direction and the z direction. For each laser line, the position of the laser line is detected for a number of measur- ing points on the line. The position of the measuring point on the sensor in the y direction corresponds to the position in the y direction of the point on the object. The position in the z direction of the measuring point on the sensor corresponds to the position in the z direction of the point on the object. The first three laser lines in figure 2 are shorter than the other seven lines. The reason for this is that the first three laser lines originate from side 1 a of the object, which has a shorter extension in the y direction, and that the other lines originate from the side 1 b of the object, which has a longer extension in the y direction.

The position of the point in the x direction is obtained by knowing the movement of the sensor in the x direction during the measuring. The sensor detects the position of the measuring point in the unit pixel. A pixel corresponds to the two-dimen- sional resolution of the sensor. Accordingly, a number of measuring points having two coordinates (y, z) in the form of a num- ber of pixels, are obtained from the sensor. Those measurements have to be calibrated later and transformed to the SI unit meter, or preferably, to the unit millimeter. The calibration of the sensor is performed by placing an object with a known geometry into the scanning system and reading its surface. For each of the laser lines, a large number of measuring points are read. In dependence of the read measurements values for the coordinates (y, z) and known values for the coordinates of the surface of the object, a number of calibration constants are calculated, which can be used for calibration of the measuring values and transforming them from pixels to millimeter. In this embodiment example, the calibration constant is calculated by dividing the known values of the coordinates by the measuring values for the coordinates. Later, when a measuring value is to be calibrated, the measuring value is multiplied by the calibration constant.

It is not enough to use the same calibration constant for all the laser lines or for all the measuring points on the same line, due to the fact that the sensor behaves differently depending on where on the sensor the measuring occurs. Therefore, for each laser line a calibration table with a large number of calibration constants is established. Accordingly, each of the laser lines has its own table with calibration constants. If there does not exist any values (y, z) in the calibration tables that exactly cor- respond to the values on y and z for the measuring point to be calibrated, two or three neighboring points are chosen, and the calibration value is interpolated based on the calibration constants for the neighboring points.

When the measuring is finished, there are a large number of measuring values for each laser line, which together correspond to a part of the surface of the object, a so-called surface part. A problem in connection with the calibration is how to know which laser line belongs to which calibration table. A matching be- tween laser lines and calibration tables has to be performed. One way of solving this problem is to try all the tables until the combination of laser lines and calibration tables that presents the best continuing surface, is found, i.e. a surface that has no abrupt changes in the vertical direction (the z direction) at the transitions between the surface parts.

The calibration is performed according to the following , after finishing the measuring, the coordinates (y, z) for each of the surfaces are calculated by means of a plurality of, or all of, the calibration tables. Thereafter, the vertical distance (z direction) between neighboring surfaces for different combinations of tables are calculated. The combination of tables that provides the minimum difference in heights between the surfaces is estimated and is later used for carrying out the calibration. This estimation is, for example, carried out by means of some known minimizing method, such as the least-square method. For the lines originating from the side 1 a, which is turned away from the sensor, it is necessary to compensate for the movement in the z direction before the calibration and matching of the calibration tables can be made.

The calibration and the other calculations are advantageously performed by software executed on a computer. The calculation unit 7 comprises a processor and memories and can either be mounted in direct connection to the other units in the scanner system or is executed in an external computer.

The invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims. For example, the carrier unit can be moved a distance that is longer than the distance between the laser lines so that the measurements overlap each other, and the overlapping measurements are used for determining which laser line and calibration table belongs to each other.

Claims

1 . A scanner system arranged for determining coordinates of the surface of a three-dimensional object (1 ), wherein the scan- ner system comprises a lighting unit (2) arranged for generating a line of visible light intended to be reflected by the object, a sensor (5) arranged for detecting the line reflected from the object, and a calculating unit (7) adapted for calculation of the coordinates in dependence of the detected line, characterized in that the lighting unit (2) is arranged so that it simultaneously generates a plurality of visible lines (3a-3c) intended for being reflected by different parts of the object, that the sensor is arranged for detecting the reflected lines (6a-6c), and that the calculating unit (7) is adapted for calculating the coordinates of the surface in dependence of the detected lines.

2. A scanner system according to claim 1 , characterized in that the scanner system is arranged such that the generated lines illuminate the object with essentially parallel lines.

3. A scanner system according to claim 1 or 2, characterized in that the lighting unit (2) is arranged for simultaneously generating at least three visible lines (3a-3c) intended for being reflected by different parts of the object.

4. A scanner system according to any of the claims 1 -3, characterized in that the sensor (5) and the lighting unit (2) are arranged so that the angle between the measuring direction of the sensor and the lighting unit is between 20° and 50°.

5. A scanner system according to any of the previous claims, characterized in that the lighting unit (2) and the sensor (5) are mounted on a carrier unit (10), wherein the carrier unit on one hand is arranged moveable in one direction (x) along the object and on the other hand is arranged rotateable in relation to the object.

6. A scanner system according to claim 5, characterized in that the carrier unit (10) is arranged moveable in a direction along the longitudinal axis of the object and that the carrier unit is arranged rotateable about an axis (14), which is essentially parallel to the longitudinal axis of the object.

7. A scanner system according to claim 5 or 6, characterized in that the carrier unit (10) is arranged adjustable in at least two predefined angular positions corresponding to the position of two sides of the object.

8. A scanner system according to any of the previous claims, characterized in that it comprises a reflecting member (9) ar- ranged for reflecting at least the main part of the lines generated by the lighting unit in a direction towards the object.

9. A scanner system according to any of the previous claims, characterized in that it comprises a reflecting device (16) ar- ranged for reflecting one of the lines reflected by the object in a direction towards the sensor.

10. A scanner system according to claim 9, characterized in that said reflecting device (16) is arranged for reflecting the line or lines reflected from the short side of the object in a direction towards the sensor.

1 1 . A scanner system according to claim 9 or 10, characterized in_. that it comprises a calibration means adapted for calibrating each line separately in dependence of a number of calibration tables.

12. A method for determining the coordinates of a surface of a three-dimensional object, comprising simultaneously generating a plurality of lines of visible light intended for illuminating different parts of the object, reflecting the lines by the object, detect- ing the lines reflected by the object, and calculating the coordinates for the surface in dependence of the detected lines.

13. A method according to claim 12, wherein at least three visi- ble lines intended for being reflected by different parts of the object are generated.

14. A method according to any of the claims 12 and 13, wherein the generated lines illuminate the object with essentially parallel lines.

15. A method according to any of the claims 12-14, wherein the lines are moved in relation to the object simultaneously as the reflected lines are detected and that the distance, (+in) which the lines are moved, essentially correspond to the distance between the lines when they are reflected by the object.

16. A method according to any of the claims 12.15, wherein the lines are moved along a first side of the object and the coordi- nates for the first side are calculated, wherein the lines are moved along a second side of the object and the coordinates for the second side are calculated.

17. A method according to any of the claims 12-16, wherein each of the lines is calibrated separately using a number of calibration tables, each calibration table being adapted to one of the lines.