Light-integrating rangefinding device and method
A rangefinding device and a method for determining the range of an object from a rangefinding device are provided. A train of light pulses each having an emission time and a pulse duration is generated. The pulse duration is set to twice the round-trip time to a maximum range of the device. The light pulses are reflected back toward the device by the object and detected according to three time intervals, respectively determined by a background gate, a ranging gate and a pulse energy gate. The light energy received during each interval is integrated and the integrated light value corresponding to the ranging gate is normalized using the values from the other two intervals. The range of the object is determined from the normalized ranging measurement and calibration data.
1. A method for optically measuring a range R of an object from a rangefinding device, comprising the steps of:
a) emitting a train of light pulses from said rangefinding device toward said object for reflection thereby, each of said light pulses having an emission time and having a pulse duration corresponding to a round-trip time to a maximum range;
b) detecting light received by said rangefinding device during three time intervals of a same gate duration, said gate duration corresponding to twice the pulse duration, said time intervals being determined by:
a background gate closing at the emission time of one of said light pulses;
a ranging gate centered on the emission time of another one of said light pulses; and
a pulse energy gate opening at the emission time of yet another one of said light pulses;
c) integrating light detected during each of said time intervals, thereby obtaining an integrated light value for each of said gates;
d) normalizing the integrated light value for said ranging gate using the integrated light values for the background and pulse energy gates, thereby obtaining a normalized ranging measurement; and
e) determining said range R of the object from said normalized ranging measurement and calibration data.
2. The method according to claim 1 , wherein the integrating of step c) is performed optically during to detecting of step b).
3. The method according to claim 1 , wherein the integrating of step c) is performed electronically or numerically after the detecting of step b).
4. The method according to claim 1 , wherein the normalizing of step d) comprises performing the calculation:
M
R
=
M
2
-
M
1
M
3
-
M
1
where M R is the normalized ranging measurement value, M 1 is the integrated light value for the background gate, M 2 is the integrated light value for the ranging gate and M 3 is the integrated light value for the pulse energy gate.
5. The method of claim 1 , wherein the detecting of step b) is performed for a plurality of said light pulses, the integrating of step c) cumulating light relative to said plurality of light pulses within each of said time intervals.
6. The method of claim 5 , wherein the detecting of step b) comprises:
detecting light received within the background gate for a number N of light pulses;
detecting light received within the ranging gate for a number N of subsequent light pulses; and
detecting light received within the pulse energy gate for a number N of subsequent light pulses.
7. A rangefinding device for optically measuring a range R of an object therefrom, comprising:
an emitter module for emitting a train of light pulses toward said object for reflection thereby, each of said light pulses having an emission time and having a pulse duration corresponding to a round-trip time to a maximum range;
a receiver module for detecting light received thereby during three time intervals of a same gate duration, said gate duration corresponding to twice the pulse duration, said time intervals being determined by a background gate closing at the emission time of one of said light pulses, a ranging gate centered on the emission time of another one of said light pulses, and a pulse energy gate opening at the emission time of yet another one of said light pulses;
integrating means for integrating light detected during each of said time intervals, thereby obtaining an integrated light value for each of said gates;
normalizing means for normalizing the integrated light value for said ranging gate using the integrated light values for the background and pulse energy gates, thereby obtaining a normalized ranging measurement; and
determining means for determining said range R of the object from said normalized ranging measurement and calibration data.
8. The rangefinding device according to claim 7 , wherein the emitter module comprises:
a light source assembly comprising at least one light source for generating said train of light pulses; and
emitter optics for shaping the train of light pulses from the at least one light source into at least one beam having desired optical characteristics.
9. The rangefinding device according to claim 7 , wherein the receiver module comprises:
a light detecting assembly for detecting light during said time intervals; and
light receiving optics for directing light received at said receiver module onto the light detecting assembly.
10. The rangefinding device according to claim 9 , wherein the light detecting assembly comprises a light sensor and a shutter controlling the exposure of the light sensor to the light received at said receiver module according to said time intervals.
11. The rangefinding device according to claim 10 , wherein said light sensor comprises a single photosensitive element.
12. The rangefinding device according to claim 10 , wherein said light sensor comprises a plurality of photosensitive elements forming a linear or two-dimensional array, each of said photosensitive elements performing an individual rangefinding function.
13. The rangefinding device according to claim 10 , wherein the integrating means comprise a light integrating function of said light sensor.
14. The rangefinding device according to claim 13 , comprising a processing unit in communication with the receiver module for receiving the integrated light value for each of said gates from said light sensor, the normalizing means and determining means being components of said processing unit.
15. The rangefinding device according to claim 7 , comprising a processing unit in communication with the receiver module for receiving therefrom signals representative of the light detected thereby, the integrating means, normalizing means and determining means being components of said processing unit.
16. The rangefinding device according to claim 7 , further comprising a control unit in communication with the emitter module and receiver module, said control unit generating control signals for controlling the emission of the light pulses and for controlling the detection of light during said time intervals.
17. The rangefinding device according to claim 7 , wherein the normalizing means perform the calculation:
M
R
=
M
2
-
M
1
M
3
-
M
1
where M R is the normalized ranging value, M 1 is the integrated light value for the background gate, M 2 is the integrated light value for the ranging gate and M 3 is the integrated light value for the pulse energy gate.
18. The rangefinding device according to claim 7 , wherein the receiver module detects light within each of said time intervals for a plurality of said light pulses, the integrating means cumulating the light detected within each of said time intervals.
19. The rangefinding device according to claim 18 , wherein the receiver module is adapted to detect light received within the background gate for a number N of light pulses, detect light received within the ranging gate for a number N of subsequent light pulses, and detecting light received within the pulse energy gate for a number N of subsequent light pulses.