3D距離画像センサ「アンフィニソレイユ」FX10s

The theor of measurement.

This sensor measures the distance between the sensor and the target by checking the time for the emitted 　 laser light to travel to and from the target (time of flight).

The light travels 30 cm in one nanosecond (one billionth of a second), so if the distance between the sensor and target changes by 15 cm (30 cm for a round trip), the difference of traveling time of light emitting and receiving changes by one nanosecond.

This sensor measures the time difference at the smallest unit of about 30 picoseconds (one trillionth of 30 seconds).(Fig. 1)

Laser scanning

The 2D scanning mirror (EcoScan) scans the laser beam by the way of Lissajous scanning up and down and right to left, and measures the distance at each scanning angle. EcoScan can obtain a large scanning angle with small amount of electric power utilizing resonance driving. In the case of this sensor, both horizontal and vertical scanning is made in the range near to the resonance frequency. The resonance frequency of vertical direction differs from that of horizontal direction, so if the both are combined, the frequency locus will be as shown by Fig.2. When the lower left is the origin of scanning, the coordinate to which the light reaches after t seconds can be calculated as follows.

And it returns to the origin after the cycle which is determined by the combination of X and Y scanning cycle. A table with which the coordinates and times to emit the laser beam can be obtained is to be prepared beforehand, and by emitting the laser bean at the best timing and measuring the distance, the distance of each coordinate (scanning angle) can be measured and the distance and image can be obtained.

This system is not influenced by ambient light.

The ranging method used in our Laser ranging / image sensor is flight time ranging, which obtains the distance to the target measuring the traveling time of the emitting laser light from the sensor to the target and the scattered light received by photo sensor back from the target.
The photo sensor used in this Laser ranging / image sensor has an extremely high sensitivity. If it receives strong ambient light, noise will be generated. For ranging, the level of receiving scattering light (S) must be higher than the noise level (N).
Therefore we adopted the method of coaxial optical system. There are other methods like the method of separated optical system or the method of CCD/CMOS image sensor and so on. In the case of the method of coaxial optical system, with Eco Scan the direction of laser beam projection and the field of view of the photodiode can be concentrated on each measuring point respectively, thus it is possible to have the signal reception under very high level scattering light (S) and to keep the noise level (N) minimized, and this makes it possible to range the distance under the sunlight. (Fig. 4)
In the case of separated optical system sensor which has two independent optical systems for each light emitting and receiving, a filed of view to cover a wide scanning area is required, and so a large volume of ambient light comes to the photo sensor, and consequently the noise level(N) will be increased. (Fig. 5)
And in the case of method which uses an image sensor with ranging capability, [CCD/CMOS image sensor method] the field of view per one pixel of photo diode is narrow, and the noise level (N) can be lower, however due to wide-area laser light emitting at a time, the irradiated light volume per one measuring point becomes smaller, and it is impossible to obtain a high enough scattering t light level(S). (Fig. 6)