Three-dimensional imager

Abstract

A three-dimensional (3D) measuring system and a method of determining a distance is provided. A three-dimensional (3D) measuring system includes a projector operable to project a pattern of light onto an object. A camera is operable to image the projected pattern of light. An electrical power distribution network is operable to receive alternating current having a line frequency. A control system is operable to set an exposure time of the camera to a positive integer divided by twice a line frequency. A processor is operable to determine three-dimensional (3D) coordinates of a point on the object based at least on the projected pattern of light and on the imaged pattern of light.

What is claimed is: 
     
         1 . A device comprising:
 a projector operable to project a pattern of light onto an object;   a camera operable to image the projected pattern of light;   an electrical power distribution network operable to receive alternating current having a line frequency;   a control system operable to set an exposure time of the camera to a positive integer divided by twice the line frequency; and   a processor operable to determine three-dimensional (3D) coordinates of a point on the object based at least on the projected pattern of light and on the imaged pattern of light.   
     
     
         2 . The device of  claim 1 , wherein the pattern of light has light levels that vary sinusoidally in space. 
     
     
         3 . The device of  claim 1 , wherein the projector is operable to project three sinusoidal patterns of light, each being shifted in space with respect to the other sinusoidal patterns. 
     
     
         4 . The device of  claim 1 , wherein the control system is further operable to trigger exposure of the camera at once per half-period, the half-period being a reciprocal of twice the line frequency. 
     
     
         5 . The device of  claim 4 , wherein the control system is further operable to detect a background light level. 
     
     
         6 . The device of  claim 5 , wherein the control system is further operable to trigger exposure when, during the half-period, a change in the background light level is a minimum. 
     
     
         7 . The device of  claim 5 , wherein the control system is further operable to trigger exposure when, during the half-period, the background light level is a minimum. 
     
     
         8 . The device of  claim 5 , wherein the control system is further operable to reconstruct a waveform of the detected background light level by sampling the background light level with an optical detector, the sampling performed at a sampling period. 
     
     
         9 . The device of  claim 8 , wherein the optical detector includes one or more photodetectors included in a photosensitive array of the camera. 
     
     
         10 . The device of  claim 8 , wherein the sampling period is longer than the half-period. 
     
     
         11 . The device of  claim 8 , wherein the optical detector is a single-element photodetector. 
     
     
         12 . The device of  claim 8 , wherein the device further includes an enclosure to which the projector, the camera, and the electrical power distribution network are coupled. 
     
     
         13 . The device of  claim 12 , wherein the optical detector is a single-element photodetector operable to move independently of the enclosure. 
     
     
         14 . The device of  claim 1 , wherein the camera further includes an optical filter element or an optical filter coating operable to reduce entry into the camera of wavelengths different from wavelengths in the projected pattern of light. 
     
     
         15 . A method comprising:
 projecting with a projector a pattern of light onto an object;   imaging with a camera the pattern of projected light;   determining a line frequency received by a background light;   setting an exposure time of the camera to a positive integer divided by twice the line frequency;   determining three-dimensional (3D) coordinates based at least in part on the projected pattern of light and the imaged pattern of projected light; and   storing the 3D coordinates.   
     
     
         16 . The method of  claim 15 , further comprising triggering the camera once per half-period, the half-period being a reciprocal of twice the line frequency. 
     
     
         17 . The method of  16 , further comprising measuring a background light level. 
     
     
         18 . The method of  claim 17 , further comprising triggering exposure when, during the half-period, a change in the background light level is a minimum. 
     
     
         19 . The method of  claim 17 , further comprising triggering exposure when, during the half-period, the background light level is a minimum. 
     
     
         20 . The method of  claim 17 , wherein the measuring of the background light level is made by an optical detector not included into the camera.