Time of flight camera unit and optical surveillance system
A time of flight, TOF, camera unit for an optical surveillance system and an optical surveillance system comprising such a TOF camera is disclosed. The TOF camera unit comprises a radiation emitting unit for illuminating a surveillance area defined by a first plane, a radiation detecting unit for receiving radiation reflected from said surveillance area and for generating a three-dimensional image from said detected radiation, and at least one mirror for at least partly deflecting said emitted radiation into at least one second plane extending across to said first plane and for deflecting the radiation reflected from said second plane to the radiation detecting unit. The TOF camera and the at least one mirror may be arranged on a common carrier element.
1. A time of flight (TOF) camera unit for an optical surveillance system, said TOF camera unit comprising:
a radiation emitting unit for emitting a modulated light for illuminating a surveillance area, wherein the surveillance area is defined by a first plane and a second plane and wherein a first portion of the modulated light illuminates the first plane and a second portion of the modulated light illuminates the second plane;
a radiation detecting unit for receiving the first portion and the second portion of the modulated light reflected from said surveillance area; and
at least one mirror for deflecting the second portion of the modulated light onto said second plane and for deflecting the modulated light reflected from said second plane to the radiation detecting unit, wherein the radiation detecting unit includes an array of pixels configured to detect a phase shift in the modulated light reflected from each of the first plane and the second plane and wherein the radiation detecting unit is configured to generate a three-dimensional image based on a first optical path length determined from said detected phase shift in the modulated light reflected from the first plane and based on a second optical path length determined from said detected phase shift in the modulated light reflected from the second plane, wherein the second optical path length is corrected by an additional optical path length defined by a geometric position of the at least one mirror with respect to the TOF camera unit and a background of the surveillance area.
2. The TOF camera unit according to claim 1 , wherein said radiation emitting unit comprises at least one light emitting diode, LED, or infrared radiation emitting diode, IRED.
3. The TOF camera unit according to claim 1 , wherein said radiation detecting unit comprises a phase sensitive detector chip and a signal processing unit for evaluating outputs of said detector chip.
4. The TOF camera unit according to claim 3 , wherein said signal processing unit is operable to define and evaluate a first depth level representing the area directly illuminated by said radiation emitting unit, and at least one second depth level representing the area illuminated by said radiation emitting unit via said at least one mirror,
wherein said signal processing unit is further operable to combine the images corresponding to the first and second depth levels for generating a three-dimensional image of the total surveillance area.
5. The TOF camera unit according to claim 1 , further comprising a carrier element, wherein said at least one mirror is held in a predetermined position with respect to said TOF camera by means of said carrier element.
6. The TOF camera unit according to claim 1 , wherein a viewing angle of said radiation detecting unit is larger than needed for monitoring said surveillance area, and wherein said at least one mirror is located in a peripheral region of said viewing angle.
7. The TOP camera unit according to claim 1 , wherein an aperture of said radiation emitting unit is larger than needed for illuminating said surveillance area, and wherein said at least one mirror is arranged in a way that it deflects a peripheral portion of the modulated light.
8. The TOF camera unit according to claim 1 , wherein said radiation emitting unit and said radiation detecting unit are arranged within a common camera housing and wherein a plurality of mirrors is arranged symmetrically around said camera housing.
9. The TOF camera unit according to claim 1 , wherein said radiation emitting unit comprises an array of light emitting diodes, LED, or infrared radiation emitting diodes, IRED, which are arranged on a non-planar substrate and said radiation detecting unit comprises an array of photonic mixer detectors, PMD, which are arranged on a non-planar substrate.
10. An optical surveillance system comprising:
a time of flight, TOF, camera for three-dimensionally monitoring an object located in front of a background in a surveillance area, the TOF camera having an emitting unit and a detector unit, the emitting unit configured to add a modulation to a radiation, defining a modulated radiation;
at least one mirror element for deflecting the modulated radiation emitted from the emitting unit of the TOF camera to said surveillance area and for deflecting the modulated radiation reflected by the surveillance area to the detector unit of the TOF camera;
a control unit for calculating a three-dimensional image of the surveillance area from the modulated radiation received by said detector unit, wherein the control unit detects a distance between the emitting unit and the surveillance area as a function of a phase shift of the modulation present on the modulated radiation reflected from the surveillance area with respect to the modulated radiation emitted from the emitting unit and as a function of an additional optical path length defined by a geometric position of the at least one mirror with respect to the TOF camera unit and the background.
11. The optical surveillance system according to claim 10 , wherein said control unit is further operable to evaluate said three-dimensional image and to output a safety switching signal in response to a result of the evaluation.
12. The optical surveillance system according to claim 10 , wherein said emitting unit comprises at least one light emitting diode, LED, or infrared radiation emitting diode, IRED.
13. The optical surveillance system according to claim 10 , wherein said detector unit comprises a phase sensitive detector chip and a signal processing unit for evaluating outputs of said detector chips.
14. The optical surveillance system according to claim 13 , wherein said signal processing unit is operable to define and evaluate a first depth level representing the area directly illuminated by said emitting unit, and at least one second depth level representing the area illuminated by said emitting unit via said at least one mirror,
wherein said signal processing unit is further operable to combine the images corresponding to the first and second depth levels for generating the three-dimensional image of the surveillance area.
15. The optical surveillance system according to claim 10 , further comprising a carrier element, wherein said at least one mirror is held in a predetermined position with respect to said TOF camera by means of said carrier element.
16. The optical surveillance system according to claim 10 , wherein a viewing angle of said detector unit is larger than needed for monitoring said surveillance area, and wherein said at least one mirror is located in a peripheral region of said viewing angle.
17. The optical surveillance system according to claim 10 , wherein an aperture of said emitting unit is larger than needed for illuminating said surveillance area, and wherein said at least one mirror is arranged in a way that it deflects a peripheral portion of the modulated radiation.
18. The optical surveillance system according to claim 10 , wherein said emitting unit and said detecting unit are arranged within a common camera housing and wherein a plurality of mirrors is arranged symmetrically around said camera housing.
19. The optical surveillance system according to claim 10 , wherein said emitting unit comprises an array of light emitting diodes, LED, or infrared radiation emitting diodes, IRED which are arranged on a non-planar substrate and said detecting unit comprises an array of photonic mixer detectors, PMD), which are arranged on a non-planar substrate.