Ranging three-dimensional laser imager and method

• US 6,448,572 B1
• Filed: 09/29/1999
• Issued: 09/10/2002
• Est. Priority Date: 09/29/1999
• Status: Expired due to Term

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Innovative Technology Licensing LLC
• Inventors: Tennant, William E., Tomasini, Alfredo
• Primary Examiner(s): Le, Que T.
• Assistant Examiner(s): Luu, Thanh X.
• Application Number:
  US09/408,329
• Time in Patent Office: 1,077 Days
• Field of Search: 250/208.1, 250/559.38, 356/4.01, 356/5.01, 356/5.05, 356/5.04, 356/5.07, 356/5.08, 356/141--14, 348/135, 702/159
• US Class Current: 250/559.38
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4863 Detector arrays, e.g. charge-transfer gates

Abstract

A method and apparatus three-dimensionally images a subject scene by first illuminating it with a laser pulse, then receiving reflected light from the scene using an optical system and a pixellated array or photodetectors operating in a linear mode. The distances to the various surfaces in the scene are determined by determining the relative times of arrival of the reflected photons at each pixel on the photodetector array. Based on the light detected and its time of arrival at each pixel, a three dimensional image is constructed and displayed. High sensitivity photodetectors operating in a linear, non-geiger mode are preferably integrated with a high-gain, fast charge amplifier and a timing circuit at each pixel, enabling image acquisition in as few as one pulse. A multi-pulse embodiment allows more accurate “vernier” depth measurement, with a small number of pulses.

Claims

1. A method of imaging an object, comprising the steps of:

emitting a first pulse of light from a light source toward the object;

a predetermined interval after emitting said first pulse, emitting a second pulse of light toward the object;

arranging a photodetector array of multiple photodetector pixels to receive reflections of said first and second pulses;

detecting the first arrival at any of said multiple photodetector pixels of reflected light returned from the object;

measuring, for each of multiple photodetector pixels, an elapsed time between a time of said first arrival until a later time of a second return, said second return at each pixel being the return of light from said second pulse after reflection from the object; and

constructing an image of the object based upon the respective elapsed times measured for said multiple pixels;

wherein said predetermined interval is shorter than the round trip travel time for light from the light source to the object and back to the photodetector array.

2. The method of claim 1, wherein said photodetector array is operated in a linear, non-Geiger mode.

3. The method of claim 1, wherein the step of measuring the elapsed time comprises:

amplifying signals from said photodetector with a cascode charge amplifier having a transient rise time which is substantially independent of the amplitude of the signal;

starting a timing circuit at a start time based upon the earliest detection of reflected light returned from the object;

stopping said timing circuit at a stop time upon the detection of a return of said second pulse after reflection from the object; and

reading the timing circuit to determine the time