Wide angle laser beams can detect and measure the range to people, trees and other safety critical objects from moving aerial or ground based platforms.
We've been experimenting with a new version of our SF10 laser altimeter to see what happens when we change the normally narrow, parallel laser beam into a wider, fan shape and align it horizontally or with a downwards tilt. There is a practical limit to the wide direction (major axis) of about 30 degrees but any angle from zero to thirty degrees is attainable. The best combination of range and sensitivity is found using a 10 x 3 degree beam pattern that can detect a person more than 10m away.
The two pictures above show the SF10 laser unit and an example of the modified laser beam pattern. The intensity, and therefore the detection sensitivity, is pretty uniform across the beam so even obstacles right at the edges give a good return signal. We're using time-of-flight technology to work out the distance and the unit has I2C, serial and analog interfaces.
The real purpose of this blog post is to ask the knowledgeable members of this forum for feedback about possible applications for wide laser beams, used either stand alone or in multiples. I admit that this is not going to be the ideal solution to every problem. Instead, I hope to use your feedback as a sanity check to see if we're going in the right direction with this technology.
Thanks, LD
Comments
No kidding. I work in a manufacturing facility, and do a lot of work around the house (auto-repair, etc.) and ever since I lost my hair, you can't believe how often I bang my head on something compared to what I used to. :D
I have been using sonars for just this purpose, having high refresh rates with low processing power.
The problem with trying to scan using a narrow beam sensor is that the overall refresh rate will be way too small for reactive (or reflex) avoidance.
I have played around with the LIDAR from XV-11 Neato robotics (very similar to the RPLidar dev kit) and even with a sensor that can take 2000 readings a second you end up with <8Hz 360° refresh rate and this is only a planar scan.
If these wide angle sensors can run at 16-32Hz @ 10m max range without interfering with each other and with fewer problems outdoors than non time of flight systems, these would make a great upgrade for the ultrasonics I am currently using.
@Laser Developer thanks for you reply:). Good to know that noise and detection ability of the sonar could be a problem. When we get further in our development I might ping you again.
@Chris Card thanks for the link, very interesting reading:). I think it is a bit too technical for my brain, we are looking for products of the shelves which we can integrate to. But I have saved to article for our engineers when we get a bit further in our roadmap.
Hi Jake. Perhaps you're right, but consider that a static laser sensor is smaller, lower weight, more reliable (no moving parts), responds much faster than a scanning laser and has an easier data interface.
A laser is simply a source of light, just like an LED or incandescent lamp. The reasons for using a laser to measure distance relate more to its high speed than to the collimation properties of its beam.
The idea behind using static sensors for reflex response and scanning lasers for mapping comes from biological systems that offer good models for autonomous processes. All multi-cellular creatures use more than one sensing technology because it is the most efficient way of handling the data. For example, we humans regularly use our eyes for mapping but rely on touch (often just the hairs on our skin) for reflex "collision avoidance".
I think de-focusing the beam is completely defeating the purpose of using a laser. Since it's easy enough to scan it I think you're missing the boat.
I found the article from Photonics about wire detection that I mention in my previous post. Here's the LINK.
It seems that I did not correctly remember the details of its operation. The wire detection system transmits an AM modulated waveform and measures phase shift to find the range.
Hi Ken, an interesting application.
For the additional range and a particularly uncooperative target, the best laser beam pattern might be a bit narrower - say <5 degrees. The trick would be to align the beam with the camera so that the operator knows exactly where the laser is (or to use a small red or green aiming laser) and then "grab" readings as the drone moves around in proximity to the cables, latching the last known good result.
I can't speak for all ultrasonic devices, but at one time we manufactured ultrasonic range finders and we would never have recommended them for measuring to a narrow cable that's 15m away. The return signal would be too small, especially with all the wind and noise around a drone.
@ Laser Developer. We do power line inspections with drones. Here we need "spotters" from several positions depending on the inspection since it can be very difficult for the pilot to estimate how close the drone is to the power line when not close to a tower. Even when he has live video. Here it would be great to read out the distance via osd to the closest obstacle. We have considered using sonar for this application. They also support wide beams and range up to 8 meters. In our case we would like range up to about 15 meters. When we do not need sub 50cm precision are there any advantages of using Laser Range solutions over cheaper Sonar solutions?
Your products look very interesting by the way:)!
Very interesting Rob, thanks for the detailed feedback.
@Juraj, I'm using an SF/02 sensor. The whole thing is based on Arducopter, which is of course open source. This work was funded by a company, but it all is going back into open source. My work so far is in this branch here:
https://github.com/R-Lefebvre/ardupilot/tree/Object_Avoidance_1
This project cannot be taken to completeness without further funding though. It's a pretty big undertaking.
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