Method and device for triangulation-based distance measurement
Some embodiments of the invention include a method for determining distances to an object to be measured based on the principle of triangulation, comprising generating and emitting a measuring light beam, directing the measuring light beam to the object to be measured, detecting a reflection of the measuring light from the object with respective pixels of an image sensor during a defined detection sequence (t 0 -t e ) and deriving distance information based on the detected reflection. The detection sequence (t 0 -t e ) comprises a number of at least two exposure sub-sequences each defining a particular exposure period and saturation limit for the pixels of the sensor, wherein a successive exposure sub-sequence comprises a higher saturation limit than its prior exposure sub-sequence and each saturation limit defines a maximum charging level of the pixels for the respective exposure sub-sequence.
1. A method for determining distances to an object to be measured based on the principle of triangulation, comprising:
generating and emitting a measuring light beam,
directing the measuring light beam to the object to be measured,
detecting a reflection of the measuring light from the object with respective pixels of an image sensor during a defined detection sequence, and
deriving distance information based on the detected reflection;
wherein the detection sequence comprises a number of at least two exposure sub-sequences each defining a particular exposure period and saturation limit for the pixels of the image sensor, wherein
a successive exposure sub-sequence comprises a higher saturation limit than its prior exposure sub-sequence and
each saturation limit defines a maximum charging level of the pixels for the respective exposure sub-sequence,
the pixels are at least partly exposed by the reflected measuring light whereby the charge of each exposed pixel changes, and
the charge of each pixel reaching at least one of the maximum charging levels during the detection sequence is limited or reset according to the respective saturation limit for the period of the corresponding exposure sub-sequence.
2. The method according to claim 1 , wherein
defining the exposure periods and saturation limits so that a final total charge for substantially every pixel is below a maximum saturation level defined by a final of the exposure sub-sequences.
3. The method according to claim 1 , wherein
providing the exposure periods of the exposure sub-sequences with equal lengths of time.
4. The method according to claim 1 , wherein
providing the measuring light beam by a defined number of light pulses corresponding to the number of exposure sub-sequences of the detection sequence and
temporally adjusting the exposure sub-sequences and the light pulses so that each light pulse is emitted and/or detected during one respective exposure period, wherein
successive of the light pulses for the detection sequence are generated with decreasing pulse durations, wherein each pulse duration is temporally shorter than the respective exposure period.
5. The method according to claim 1 , wherein
the image sensor is designed as a high dynamic range (HDR) sensor and in particular provides the detection sequence.
6. The method according to claim 1 , further comprising
focussing measuring light regarding a first direction orthogonal to an emitting direction and
diffusing the measuring light regarding a second direction orthogonal to the first direction and to the emitting direction,
wherein a vertically focused and horizontally extended stripe of light is provided.
7. The method according to claim 1 , wherein
generating and emitting the measuring light beam with a spatial coherence in the first direction and incoherent regarding the second direction, wherein the measuring light beam comprises one spatial ground mode regarding the first direction and more than one spatial modes regarding the second direction.
8. The method according to claim 1 , wherein
the detection sequence and the light pulses are designed so that
an illumination by the measuring light beam regarding a bright pixel of the image sensor causes a charging level for the bright pixel below a maximum saturation limit, and
an illumination by the measuring light beam regarding a dark pixel of the image sensor causes a charging level for the dark pixel above a defined signal-to-noise threshold.
9. A non-transitory computer program product having computer-executable instructions implemented for executing and/or respectively controlling determining distances to an object according to a method according to claim 1 .
10. A triangulation-based distance measuring unit comprising:
a light emitting unit with a light source for generating measuring light and emitting a measuring beam,
a light detection unit for detecting a reflection of the light beam from an object to be measured and
a controlling and processing unit for deriving distance information based on the detected reflection,
wherein the light emitting unit and the light detection unit are arranged with known relative position and orientation to each other,
wherein
the light detection unit comprises a high dynamic range (HDR) image sensor providing a light detection sequence with a series of at least two exposure sub-sequences each defining a particular exposure period and saturation limit for pixels of the image sensor, wherein
a successive exposure sub-sequence comprises a higher saturation limit than its prior exposure sub-sequence,
each saturation limit defines a maximum charging level of the pixels for the respective exposure sub-sequence, and
the pixels are chargeable according to their exposure to the reflected measuring light so that the charge of each pixel reaching at least one of the maximum charging levels during the detection sequence is limited or reset according to the respective saturation limit for the period of the corresponding exposure sub-sequences.
11. The distance measuring unit according to claim 10 , wherein
the controlling and processing unit is adapted to control triggering the detection sequence
and control generating a number of light pulses by
the light source corresponding to the number of exposure sub-sequences for the detection sequence,
so that the exposure sub-sequences and the light pulses are temporally adjusted so that each light pulse is emitted and/or detected during one respective exposure period,
wherein
the exposure periods of the exposure sub-sequences comprise equal lengths of time, and/or
successive light pulses for the detection sequence are generated with decreasing pulse energy.
12. The distance measuring unit according to claim 10 , wherein
the light emitting unit comprises a beam forming assembly for providing the measuring beam by affecting propagation of the measuring light emittable by the light source, wherein the beam forming assembly is arranged and designed so that
the measuring light is focussed regarding a first direction orthogonal to an emitting direction, and
the measuring light is diffused regarding a second direction orthogonal to the first direction and to the emitting direction.
13. The distance measuring unit according to claim 10 , wherein the beam forming assembly comprises a cylindrical lens arranged and designed so that the focussing in the first direction is provided by the cylindrical lens and diffusing in the second direction is substantially unaffected by the cylindrical lens.
14. The distance measuring unit according to claim 10 , wherein the beam forming assembly comprises at least one array of cylindrical lenses designed and arranged so that the diffusion in the second direction is provided by refraction properties of the cylindrical lenses of the at least one array and focussing in the first direction is substantially unaffected by the at least one array, wherein the array of cylindrical lenses and the light source are designed and arranged so that the measuring beam is emittable in form of a substantially continuous line regarding its extension in the second direction.
15. The distance measuring unit according to claim 10 , wherein the beam forming assembly comprises a collimation lens arranged and designed so that the focussing in the first direction is provided by the collimation lens.
16. The distance measuring unit according to claim 10 , wherein
the light source is designed so that the measuring light is producible with a spatial coherence in the first direction and incoherent regarding the second direction, wherein the light source is designed so that the measuring light is producible comprising one spatial ground mode regarding the first direction and more than one spatial modes regarding the second direction.
17. The distance measuring unit according to claim 10 , wherein
the light source comprises a light source selected from the group consisting of:
a light-emitting diode,
a laser source, wherein the emitted light is provided as laser light and the light beam is a laser beam,
a broad area laser (BAL),
a super-luminescent diode (SLED), and
a multi-mode laser source.
18. The distance measuring unit according to claim 10 , wherein
the light source comprises a light-emitting diode having a spatial filter and/or a masking with a slit.
19. The distance measuring unit according to claim 10 , wherein
the light source comprises a light-emitting diode or laser source, wherein the light source further comprises a collimation element having asymmetric light-emitting aperture, wherein the collimation element is designed so that a length of the light-emitting aperture in the first direction is significantly smaller than in the second direction.
20. The distance measuring unit according to claim 10 , wherein
the light detection unit additionally comprises a lens, wherein the image sensor is arranged relative to the lens according to the Scheimpflug criterion, in particular considering a predefined illumination plane.