Method for measuring 3d coordinates of a surface with a portable articulated arm coordinate measuring machine having a camera

Abstract

A method for measuring three-dimensional (3D) coordinates of a surface includes providing a manually positionable articulated arm portion having opposed first and second ends, providing a measurement device coupled to the first end, the measurement device including a camera having a lens and a photosensitive array and moving the camera to first and second positions and orientations to capture first and second images. Based on data from the camera, a first set of cardinal points common to the first and images and the second images are used to form a 3D coordinates that describe the surface.

What is claimed is: 
     
         1 . A method for measuring three-dimensional (3D) coordinates of a surface comprising:
 providing a base;   providing a manually positionable articulated arm portion having opposed first and second ends, the arm portion being rotationally coupled to the base at the second end, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one angle transducer for producing an angle signal;   providing a measurement device coupled to the first end, the measurement device including a camera having a lens having a known focal length and a photosensitive array;   providing an electronic circuit configured to receive the angle signal from the at least one angle transducer for the plurality of connected arm segments and to provide data corresponding to a position and an orientation of the measurement device;   providing a processor;   sending to the processor from the electronic circuit first data corresponding to a first position and a first orientation of the perspective center of the camera lens, forming with the lens a first image of the surface on the photosensitive array, and sending a first digital signal to the processor in response;   sending to the processor from the electronic circuit second data corresponding to a second position and a second orientation of the perspective center of the camera lens, forming with the lens a second image of the surface on the photosensitive array, and sending a second digital signal to the processor in response;   finding with the processor a first set of cardinal points common to the first image and the second image based at least in part on the first digital signal, the second digital signal;   finding with the processor a first set of locations on the photosensitive array and a second set of locations on the photosensitive array, the first set of locations corresponding to the first set of cardinal points in the first image and the second set of locations corresponding to the first set of cardinal points in the second image;   determining a first set of 3D coordinates for the first set of cardinal points, the first set of 3D coordinates including 3D coordinates for each cardinal point of the first set of cardinal points, wherein the 3D coordinates for each cardinal point of the first set of cardinal points is based at least in part on the first position and the first orientation of the perspective center of the camera lens, the first set of locations, the second position and the second orientation of the perspective center of the camera lens, and the second set of locations; and   saving the first 3D coordinates.   
     
     
         2 . The method of  claim 1  wherein in the step of finding with the processor a first set of cardinal points, each cardinal point from the first set of cardinal points corresponds to a 3D feature of the surface. 
     
     
         3 . The method of  claim 1  wherein the step of finding with the processor a first set of cardinal points, at least some of the cardinal points are found by image processing of the first digital signal and the second digital signal. 
     
     
         4 . The method of  claim 3  wherein the step of finding with the processor a first set of cardinal points includes identifying an interest point. 
     
     
         5 . The method of  claim 4  wherein, in the step of finding with the processor a first set of cardinal points, the interest point is a corner. 
     
     
         6 . The method of  claim 3  wherein the step of finding with the processor a first set of cardinal points includes using a scale-invariant feature transform (SIFT). 
     
     
         7 . The method of  claim 1  wherein:
 the step of providing a measurement device further includes providing a contact probe having a probe tip; 
 the method further includes a step of placing the probe tip at a third position, the probe tip placed in contact with the surface; 
 the method further includes a step of sending to the processor from the electronic circuit third data corresponding to the third position; and 
 the method further includes determining 3D coordinates of a center of the probe tip, the 3D coordinates based at least in part on the third data. 
 
     
     
         8 . The method of  claim 1  further including steps of:
 providing a bus in electrical communication with at least one of the angle transducers and the measurement device, the bus including an encoder bus portion and a high speed bus portion; 
 providing a first serializer/deserializer coupled between the measurement device and the high speed bus portion that converts measurement data provided by the measurement device into serial form to form serial data; 
 providing a second electronic circuit configured to receive the measurement data; and 
 providing a second serializer/deserializer coupled between the high speed data portion and the second electronic circuit, the serializer/deserializer configured to convert the serial data back to the measurement data, wherein the first and second serializer/deserializers include transmit emphasis or receive equalization. 
 
     
     
         9 . The method of  claim 8  further including providing a rotary coupler having a first portion and a second portion, the second portion configured to rotate relative to the first portion, the first portion affixed to the first arm segment, the rotary coupler configured to transfer signals on both the encoder bus portion and the high speed bus portion between the first portion and the second portion. 
     
     
         10 . The method of  claim 9  wherein, in the step of providing a measurement device, the measurement device includes a laser line probe (LLP). 
     
     
         11 . The method of  claim 10  wherein, in the step of providing a measurement device, the LLP is configured to provide the measurement data in parallel form. 
     
     
         12 . The method of  claim 9  wherein, in the step of providing first and second serializer/deserializers, the first and second serializer/deserializers communicate according to at least one communication standard. 
     
     
         13 . The method of  claim 12 , wherein the at least one communication standard is selected from the group consisting of:
 Universal Serial Bus (USB) 1.0, USB 2.0, USB 3.0, Gigabit Ethernet (IEEE 802.3-2008 standard), Peripheral Component Interconnect (PCI) Express, FireWire, and Camera Link.   
     
     
         14 . The method of  claim 1 , further comprising:
 providing a color camera coupled to the first end; and   acquiring a texture with the color camera when the first image is acquired by the photosensitive array.   
     
     
         15 . The method of  claim 1 , further comprising finding a second set of cardinal points in response to determining that the at least one of the first image or second image does not overlap with the surface 
     
     
         16 . The method of  claim 1 , further comprising:
 providing a probe tip coupled to the first end;   touching the probe tip to the surface; and   determining a second set of 3D coordinates in response to touching the probe tip to the surface.