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3D LiDAR gives robots a sense of space: The development of 3D LiDAR sensors with wide scanning angles provides autonomous guided vehicles with improved object detection.

Manufacturers of robots and autonomous vehicles have to date been hampered by the disadvantages of LiDAR (light detection and ranging), the sensing technology that combines laser ranging and radar detection. Its typically narrow elevation angle when scanning has rendered it a predominantly 2D technology.

Now, a new scanning mechanism developed by Panasonic has added a third dimension to the ubiquitous sensing technology. The company has created a workable 3D LiDAR sensor, which it says will be available as samples as early as the first quarter of 2018.

THE 2D CONUNDRUM

According to Panasonic, existing LiDAR products used in advanced driver assist systems (ADAS) or autonomous vehicles suffer from the problem of having a vertical scanning angle that is fixed and too narrow. To cater for this constraint, the positioning of the sensor is optimised for the function that it has to perform.

An example of this is adaptive cruise control (ACC), where the LiDAR detects vehicles in its path, measures the distance and provides data to the control system so that speed can be adjusted in order to maintain a safe gap. In this application, a wide angle is necessary to detect any kind of vehicle from narrow motorcycles to large commercial vehicles in any position within the driving lane. Range is also important but depth of scanning angle is less so.

To scan for other features, such as road surface texture, pot-holes or overhead obstructions such as gantries or bridge parapets, other sensors are needed in order to paint a complete picture of the vehicle's 3D surroundings.

Despite the narrow vertical range, autonomous vehicle LiDAR scanners have the advantage of high-speed scanning with high accuracy in ranging.

When objects move more slowly, using a single scanner and altering the vertical scanning angle brings a new dimension to the possibilities of LiDAR

SCANNING THE VERTICAL

According to Panasonic, its new 3D LiDAR sensor measures the distance between the sensor and the target object using the round-trip travelling time of the pulsed laser beam that is projected onto the target, enabling it to accurately measure the direction of and distance to the target with a wide angle of view. It achieves this using proprietary multiple motor-driven mirrors and scanning technology.

The motorised mirror system provides the capability of scanning the laser over a 270[degrees] horizontal plane with a variable vertical angle of up to 60[degrees]. This is a defining capability in the autonomous guidance of robots and slow-moving vehicles used in agriculture and warehousing.

The variable depth scanning angle of the newly developed 3D LiDAR helps in the precise detection of objects on the ground as well as the roughness of the floor surface. In addition, the range of scanning angles and the resolution can be tailored precisely by adjusting the rotation angle and speed of the mirrors in the system. This feature gives users accuracy and flexibility to choose the most appropriate conditions for the measurement depending on their usage. This enables the wide-spread use of autonomous robots that navigate inside or outside facilities with moving objects around, including people.

Commenting on the development of the 3D system, Panasonic Industry Europe's business development manager Sudhanshu Kapoor says: "Panasonic's 3D LiDAR is a big step forward for existing LiDAR technology due to its wide-angle detection range with a vertical field of view of up to 60[degrees] as well as a distance detection of 50m. Our 3D LiDAR has IP65 protection and an M12 plug and so is capable of withstanding all types of outdoor conditions. 3D LiDAR has a lot of value in the field of autonomous navigation. With our 3D-LiDAR, we expect to collaborate together with customers to develop applications for industrial forklifts, AGVs (autonomous guided vehicles), mobile robotics, construction and smart buildings."

PRECISE CONTROL

At the heart of the new 3D LiDAR sensing system is a proprietary set of motor controlled mirrors, which Panasonic developed based on computer optical disk drive actuator technology, which employs high precision, reliable miniature motors.

The 3D LiDAR employs a single laser and moving mirror for the detection operation, with the laser light travelling along the same optical path. The mirror moves in two different optical planes through the use of two motors. The single-path design and wide angle of mirror movement enables such a wide viewing angle both vertically and horizontally.

The pulse from the laser diode is reflected from a fixed mirror to a second mirror, the position of which can be varied. One motor controls the horizontal angle while a second controls the vertical. The pulse returns along the same path to the photo detector.

VARIABLE RESOLUTION

Another factor which differentiates the 3D LiDAR from systems used in autonomous cars and for ADAS applications is the ability to vary resolution settings based on environmental factors. The resolution for most LiDAR sensors is fixed.

On the 3D LiDAR, the resolution can be varied from low resolutions for performing quick scans within a wide range for object detection to high resolutions at lower speeds for gaining more detail of the target object.

According to Panasonic, autonomous robotic systems do not need to sense objects in detail when they move on flat surfaces with fewer objects in the vicinity. In this case, the object detection sensor can be scanned at relatively high speed in accordance with the robot's speed. On the other hand, in an area with many moving people or objects, it requires high sensing resolutions with a wide angle of view. Furthermore, the sensor needs to examine the details of the object's surface that has been detected. Panasonic's 3D LiDAR can easily vary the detection settings thanks to its laser-scanning technology. Stable and time-effective operations of autonomous robots can be achieved by choosing the most suitable detection settings depending on the conditions of the areas where they will be used.

SUNLIGHT RESISTANCE

Optical systems and camera-based sensors are prone to problems in variable lighting conditions, particularly where there are shadows or strong sources of light. With agricultural and warehouse vehicles having to cope with wide ranges of strength in ambient light, it's important that the sensors are able to cope with this so that autonomous control is maintained regardless of conditions.

Panasonic has overcome this in the 3D LiDAR by reducing the noise that's induced by strong sunlight. According to Kapoor, this is achieved by making the return light follow the same path as the emitted laser.

"As a result, the newly developed 3D LiDAR can be operated with high accuracy even under a light intensity of 100,000 lux, corresponding to strong sunlight in summer-time," he concludes.
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Title Annotation:AUTONOMOUS CONTROL
Publication:Environmental Engineering
Date:Dec 1, 2017
Words:1099
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