Method and device for recording a three-dimensional distance-measuring image

• US 20040233416A1
• Filed: 02/05/2004
• Published: 11/25/2004
• Est. Priority Date: 08/06/2001
• Status: Active Grant

• Current Assignee: Rockwell Automation, Inc.
• Original Assignee: Siemens AG
• Inventors: Doemens, Gunter, Mengel, Peter
• Granted Patent: US 7,212,278 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/18 wherein range gates are used
• 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 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection

Abstract

The invention relates to methods and devices for recording three-dimensional distance-measuring images of an object surface by measuring light propagation time using a short-term integrated photodetector. For starting a light-induced pulse (1) on the transmission side, a trigger signal is produced that is at the same time used on the receiving side for opening at least one integration window (2, 21, 22) for receiving back-scattered light-induced pulses (3) with a predetermined time delay (ΔT_V). A predetermined event such as a maximum or a zero crossing is detected which, by its interval relative to the integration windows, determines a trigger delay. Said trigger delay is correlated with the light propagation time and allows calculation of the object point distance d.

Claims

1. A method for recording a three-dimensional distance-measuring image of an object by measuring light propagation times, comprising:

transmitting light-induced pulses from a light source to an object surface;

receiving backscattered light-induced pulses by a photodetector with short-term integration; and

calculating an object point distance in each case from light propagation time of the light-induced pulses, wherein

a trigger signal produced for starting a light-induced pulse is applied at a same time on a receiving side with a trigger delay that increases gradually in time increments for opening at least one integration window for receiving the backscattered light-induced pulses, and

in each predetermined trigger delay, a multiple illumination is implemented with an integration window opened for each illumination for cumulative integration of the reflected light-induced pulses.

2. The method according to claim 1, wherein

the trigger signal on the receiving side is used for the repeated opening of a single integration window for receiving the backscattered light-induced pulses,

the distance of an object point is calculated once a maximum value for an integrated voltage is reached, from the corresponding trigger delay, which is approximately equal to the light propagation time.

3. The method according to claim 2, wherein the duration of the integration window is equal to the duration of a light-induced pulse.

4. The method according to claim 1, wherein

the trigger signal on the receiving side is used for the repeated opening of a first integration window, followed by a second integration window, in each case for receiving the backscattered light-induced pulses,

the short-term integration for the two integration windows is carried out in parallel or in series with equal integration time,

the duration of the light-induced pulses is small relative to the integration time, and

the distance of the object point can be calculated if the light-induced pulse is positioned on a shared boundary between the first and second integration windows and equal amounts of the integrated voltages relating to the two integration windows are present, such that the corresponding trigger delay corresponding to the light propagation time is converted into the distance value.

5. The method according to claim 4, wherein, instead of comparing the amounts of the integrated voltages, one voltage is negatively set and a zero crossover between the two voltages assigned to successively actuated integration windows is detected.

6. The method according to claim 4, wherein photodiodes used as sensor elements are divided into two separate sections, with each section receiving a same optical intensity.

7. The method according to claim 1, wherein if a reflectivity of an object or individual object points is heavily differentiated, a number of multiple illuminations is selected such that integrated intensity values are near a saturation region for maximum number of object points.

8. The method according to claim 1, wherein light from a laser or laser diode is used for illumination.

9. The method according to claim 1, wherein the trigger delay for the first light-induced pulse of an image recording on the receiving side is equal to zero.

10. The method according to claim 1, wherein a duration of an integration window is constant.

11. The method according to claim 1, wherein the trigger delay increment is less than 0.25 nanoseconds.

12. The method according to claim 2, wherein interpolation is used to determine maximum values and/or zero crossovers of the voltage.

13. The method according to claim 12, wherein interpolation is used based on quadratic polynomials or spline functions.

14. The method according to claim 1, wherein a comparison with a previously stored reference curve with known distance (d) is carried out in order to evaluate voltages.

15. The method according to claim 1, wherein the trigger delay occurs through use of programmable delay lines.

16. A device for recording a three-dimensional distance-measuring image of an object by measuring light propagation times, comprising:

a light-induced pulse illumination with a single light source for illuminating the object surfaced;

a CMOS sensor with a plurality of sensor points as the photodetector, with pixel-based short-term integration;

a control and processing unit, that controls at least triggering on a transmission side and a receiving side and calculates distance values from voltage signals,

a delay line between the control and processing unit and the CMOS receiving sensor for preparing an incrementally adjustable trigger delay; and

trigger cables configured to the light-induced pulse illumination and to the CMOS receiving sensor.

18. The device according to claim 16, wherein the control and processing unit is integrated at least partially in an electronic unit of the CMOS receiving sensor.

19. The device according to claim 18, wherein the voltage values of photodiodes are fed in parallel or in series, then stored in interim buffer units where they are optionally fed to a difference amplifier and then to a processing unit.

17. (Canceled)