TARGET APPARATUS AND METHOD

• US 20120206716A1
• Filed: 02/29/2012
• Published: 08/16/2012
• Est. Priority Date: 02/14/2011
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Cramer, Peter G., Bridges, Robert E., Steffensen, Nils P., Steffey, Kenneth, Hoffer, John M. Jr., Mehler, Robert C., Lasley, Daniel G.
• Granted Patent: US 8,467,072 B2
• Time in Patent Office: Days
• US Class Current: 356/72
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 11/03 by measuring coordinates of points
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01C 15/004 Reference lines, planes or sectors
• CPC Class Codes: G01C 15/06 Surveyors' staffs; Movable markers
• CPC Class Codes: G01K 7/02 using thermoelectric elements, e.g. thermocouples
• CPC Class Codes: G01K 7/22 the element being a non-linear resistance, e.g. thermistor G01K7/26 takes precedence
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/74 Systems using reradiation of electromagnetic waves other than radio waves, e.g. IFF, i.e. identification of friend or foe
• CPC Class Codes: G01S 7/48 of systems according to group G01S17/00
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G02B 5/12 Reflex reflectors
• CPC Class Codes: G02B 5/122 cube corner, trihedral or triple reflector type

Abstract

A target includes a contact element having a region of spherical curvature, a retroreflector rigidly connected to the contact element, a transmitter configured to emit an electromagnetic signal, a temperature sensor disposed on the target, configured to measure an air temperature, and configured to send the measured air temperature to the transmitter.

Claims

1. A method of measurement of a target by a device, the method comprising the steps of:

providing the target, wherein the target has a target frame of reference and includes a first retroreflector and a body, the body having a spherical exterior portion that has a sphere center and a sphere radius, the body containing a cavity, the cavity sized to hold the first retroreflector, the cavity open to the exterior of the body, the first retroreflector at least partially disposed in the cavity, the first retroreflector having a first retroreflector reference point in the target frame of reference;

providing the device, wherein the device has a device frame of reference and a first light source, the device being configured to measure a distance and two angles from the device to the first retroreflector reference point;

determining at least one vector length component in the target frame of reference of a vector that extends from the first retroreflector reference point to the sphere center, the vector having a length greater than zero;

illuminating the first retroreflector with light from the first light source to provide a first reflected light that is returned to the device;

measuring, from the device to the first retroreflector reference point, a first distance and a first set of two angles based at least in part on the first reflected light, the first distance based at least in part on the speed of light over the path traveled by the light from the device to the first retroreflector reference point;

determining three orientational degrees of freedom of the target frame of reference in the device frame of reference, wherein the three orientational degrees of freedom are sufficient to fully define the orientation of the target frame of reference in the device frame of reference;

calculating three dimensional coordinates of the sphere center within the device frame of reference based at least in part on the first distance, the first set of two angles, the three orientational degrees of freedom, and the at least one vector length component; and

storing the three dimensional coordinates of the sphere center.

2. The method of claim 1, wherein:

in the step of providing the target, the first retroreflector is selected to be a cube corner retroreflector having three planar reflectors, each planar reflector capable of reflecting light, each planar reflector perpendicular to the other two planar reflectors, each planar reflector intersecting the other two planar reflectors in a common vertex, and each planar reflector having two intersection junctions, each intersection junction shared with an adjacent planar reflector for a total of three intersection junctions within the cube corner retroreflector, the cube corner retroreflector having an axis of symmetry relative to the three planar reflectors; and

in the step of determining at least one vector length component, the first retroreflector reference point is the vertex.

3. The method of claim 1, further comprising steps of:

providing a workpiece having a workpiece surface;

placing the spherical exterior portion in contact with the workpiece surface; and

calculating a three-dimensional coordinate of a point on the workpiece surface based at least in part on the three dimensional coordinates of the sphere center and the sphere radius.

4. The method of claim 1, wherein:

the step of providing the device includes providing an first camera, wherein the first camera includes a first photosensitive array and a first lens system; and

the step of determining three orientational degrees of freedom includes capturing on the first photosensitive array a first illumination pattern produced by the first reflected light, obtaining a digital representation of the first illumination pattern captured by the first photosensitive array, the determining of the three orientational degrees of freedom of the target frame of reference in the device frame of reference based at least in part on the digital representation of the first illumination pattern.

5. The method of claim 4, wherein:

in the step of providing the target, the first retroreflector is selected to be a cube corner retroreflector having three planar reflectors, each planar reflector capable of reflecting light, each planar reflector perpendicular to the other two planar reflectors, each planar reflector intersecting the other two planar reflectors in a common vertex, and each planar reflector having two intersection junctions, each intersection junction shared with an adjacent planar reflector for a total of three intersection junctions within the cube corner retroreflector, the cube corner retroreflector having an axis of symmetry relative to the three planar reflectors; and

in the step of determining at least one vector length component, the first retroreflector reference point is the vertex.

6. The method of claim 5, wherein, in the step of providing the target, the first retroreflector is provided with at least one non-reflecting mark.

7. The method of claim 5, wherein:

in the step of providing the target, the first retroreflector is provided with non-reflecting portions at each of the three intersection junctions; and

in the step of determining three orientational degrees of freedom, the capturing on the first photosensitive array the first illumination pattern produced by the first reflected light includes capturing a plurality of lines produced by the non-reflecting portions.

8. The method of claim 7, wherein the step of determining the three orientational degrees of freedom of the target frame of reference in the device frame of reference further includes calculating a slope of each of the plurality of lines, the determining of the three orientational degrees of freedom based at least in part on the calculated slopes.

9. The method of claim 8, wherein:

in the step of providing the target, the target is provided with the three planar reflectors being surfaces of a glass prism, the glass prism having a top surface, the top surface distal to the vertex, the glass prism having a refractive index, the glass prism having a normal vector to the top surface in the target frame of reference, the glass prism having an altitude length equal to the distance from the vertex to an intersection point of the axis of symmetry with the top surface, and the glass prism having a depth, the depth being the vector length component along the axis of symmetry; and

in the step of calculating three dimensional coordinates of the sphere center, the calculating is based at least in part on the refractive index, the altitude length, the normal vector to the top surface, and the depth.

10. The method of claim 9, wherein:

the step of determining at least one vector length component further includes determining two transverse lengths, the two transverse lengths being vector length components that lie in a plane perpendicular to the axis of symmetry; and

the step of calculating three dimensional coordinates of the sphere center is based at least in part on the two transverse lengths.

11. The method of claim 4, wherein:

the step of providing the target includes providing a reference feature;

the step of determining the three orientational degrees of freedom of the target frame of reference in the device frame of reference includes determining a coarse orientation of the target frame of reference in the device frame of reference; and

the determining of the coarse orientation of the target frame of reference in the device frame of reference is obtained through the use of the reference feature.

12. The method of claim 11, wherein:

in the step of providing the target, the reference feature is a reference mark, the reference mark disposed on the target in a reference orientation in the target frame of reference; and

in the step of determining the three orientational degrees freedom, the coarse orientation is based at least in part on the reference orientation.

13. The method of claim 11, wherein:

the step of providing the target includes providing a reference feature that includes reflective material;

the step of providing the device includes providing a second camera, the second camera having a second photosensitive array, a second lens system, a second light source, and a third light source, the second light source being nearer the second lens system than the third light source is to the second lens system, the second and third light sources configured so that when the second light source illuminates the first retroreflector and the region of reflective material, the total optical power received by the second photosensitive array is greater for the light reflected by the first retroreflector than by the region of reflective material, the second and third light sources further configured so that when the third light source illuminates the first retroreflector and the region of reflective material, the total optical power received by the second photosensitive array is greater for the light reflected by the region of reflective material than by the first retroreflector;

the step of illuminating the first retroreflector with light from the first light source includes illuminating the reference feature with light from the second light source to obtain a second illumination pattern on the second photosensitive array;

the step of illuminating the first retroreflector with light from the first light source includes illuminating the region of reflective material with light from the third light source to obtain a third illumination pattern on the second photosensitive array; and

the step of determining three orientational degrees of freedom includes determining the coarse orientation of the target frame of reference in the device frame of reference based at least in part on the second illumination pattern and the third illumination pattern.

14. The method of claim 11, wherein:

the step of providing the device includes providing a second camera having a second photosensitive array, a second lens system, and a second light source;

the step of providing the target includes providing a reference feature that includes a reference retroreflector;

the step of illuminating the first retroreflector further includes simultaneously illuminating the reference retroreflector and the first retroreflector with light from the second light source to obtain a second illumination pattern on the second photosensitive array; and

the step of determining the three orientational degrees of freedom of the target frame of reference in the device frame of reference further includes determining the coarse orientation of the target frame of reference in the device frame of reference based at least in part on the second illumination pattern.

15. The method of claim 11, wherein:

the step of providing the target includes providing a reference feature, the reference feature including a second retroreflector;

providing a beam steering mechanism to steer the light from the first light source;

steering the light from the first light source to the second retroreflector and measuring a second set of two angles; and

calculating the coarse orientation based at least in part on the first set of two angles and the second set of two angles.

16. The method of claim 11, wherein:

the step of providing the target (1610) includes providing a reference feature that includes a target light source;

the step of providing the device includes providing a second camera having a second photosensitive array, a second lens system, and a second light source;

the step of illuminating the first retroreflector further includes illuminating the first retroreflector with light from the second light source to obtain a second illumination pattern on the second photosensitive array and illuminating the target light source to obtain a third illumination pattern on the second photosensitive array; and

the step of determining the three orientational degrees of freedom of the target frame of reference in the device frame of reference further includes determining the coarse orientation of the target frame of reference in the device frame of reference based at least in part on the second illumination pattern and the third illumination pattern.

17. The method of claim 1, wherein the step of calculating three dimensional coordinates of the sphere center within the device frame of reference further depends on a temperature measured by a temperature sensor in thermal contact with the target.

18. A method of obtaining the characteristics of a target by a device, the method comprising the steps of:

providing the target, wherein the target has a target frame of reference and includes a first retroreflector and a body, the body containing an opening, the opening sized to hold the first retroreflector, the opening open to the exterior of the body, the first retroreflector at least partially disposed in the opening, the first retroreflector having a first retroreflector reference point in the target frame of reference;

providing a spherical contact element having a region of spherical curvature rigidly fixed with respect to the body, the spherical contact element having a sphere center and a sphere radius;

providing a device, wherein the device has a device frame of reference and a first light source, the device being configured to measure a distance and two angles from the device to the first retroreflector reference point;

providing an identifier element located on the body, the identifier element configured to store first information, the identifier element being one of a bar code pattern and a radio-frequency identification tag, the first information including one of the sphere radius and a serial number, the serial number accessed by a processor to obtain the sphere radius;

providing a workpiece having a workpiece surface;

placing the spherical contact element in contact with the workpiece surface;

illuminating the first retroreflector with light from the first light source to provide a first reflected light that is returned to the device;

measuring, from the device to the first retroreflector reference point, a first distance and a first set of two angles based at least in part on the first reflected light, the first distance based at least in part on the speed of light over the path traveled by the light from the device to the first retroreflector reference point;

reading the first information with a first reader attached to the device, the first reader being one of a bar code scanner, a radio-frequency identification reader, and a camera; and

calculating a three-dimensional coordinate of a point on the workpiece surface based at least in part on the first distance, the first set of two angles, and the first information.

19. The probe assembly of claim 18, wherein in the step of providing the target the spherical contact element and the body have the same sphere center and sphere radius.

20. A target, comprising:

a retroreflector;

a body having a spherical exterior portion, the body containing a cavity, the cavity sized to hold the retroreflector, the cavity open to the exterior of the body, the retroreflector at least partially disposed in the cavity;

a transmitter configured to emit an electromagnetic signal; and

a first actuator configured to initiate emission of the electromagnetic signal.

23. A target, comprising:

a contact element having a region of spherical curvature;

a retroreflector rigidly connected to the contact element;

a transmitter configured to emit an electromagnetic signal; and

a temperature sensor disposed on the target, configured to measure an air temperature, and configured to send the measured air temperature to the transmitter.

21. The target of claim 23, wherein the first actuator is a button.

22. The target of claim 23, further comprising a second actuator.