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We are working on a research project. We try to measure the distance from an object to some static line/pole. The area of interest is within a range of 1 to 5 meters, and the tracked object is a human.

Our desire is to precisely measure the distance with a max disparity of up to 2cm. Our region of interest is an imaginary tube with a radius of up to 40cm, but it may be less. The length of this tube is about 5 meters.

The attached pic illustrates our case - an object goes over the virtual "tube" (a region of interest, essentially). The distance (x on the pic) we would like to measure.

Region of interest

We tried stereo vision approaches, but we also want to compare results with lidar/ultrasonic sensors. Can anyone suggest some proper sensor? Our technical limit for this sensor system is a weight. This system should be less than 3 kg. Our project has flexible budget, so costs are not much of a limit.

One of the possible solutions we consider is a set of small lidar/ ultrasonic sensors. A very primitive scheme is drawn on the attached pic. Tiny same size sensors are depicted in red. Pole to which the distance we interested in is depicted in gray. enter image description here

The moving object goes over the static object, and "cuts" the beams of several of the 1D Lidars in our array. We thus know the object position with a precision of the space between Lidars in our 1D array. We have searched for various lidars to achieve this purpose, and because of the precision being tied to spacing between sensors, the following constraints arise:

  1. Something small is necessary for this purpose - a diameter of max 2cm, assuming this is still a circle-shaped sensor.
  2. Since it's tracking a moving object, a scanning frequency of, say, >30hz would be good. The range is up to 5 meters.
  3. The beam is very directional and focused so that there is no crosstalk/interference between elements of lidar array. Because we need very directional beam, FOW for one sensor should be less than 0.5 degrees. enter image description here
  4. The precision of distance from sensor to object is not important for us, we just need to know if there is an object present or not.

The closest candidate that fulfills the requirements by size is actually an ultrasonic sensor, however that has issues with focus and interference.

If anyone knows of a sensor that fulfills this purpose or can guide me to who might offer one, I would appreciate it. Thank you.

P.S.

A friend of mine posted the same question in Robotics, but we have not received any answers.

Stanislav
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  • Instead of "finding the sensor that does the job", first try to find **real world examples** that roughly do what you need/want. If you can't find any then maybe it can't be done? It might be that the system is much more complex than "just a sensor". Also, search for "range finding" and "measure distance" on this site and elsewhere. You're not the first to ask for a short range distance measurement solution and also not the first to think it can easily be solved with the right sensor while it actually cannot. – Bimpelrekkie Jul 01 '20 at 09:55
  • @Bimpelrekkie thanks for the comment. I am not experienced enough in this subject, but I can already agree with you, that this is not an easy task. Can you please suggest some examples from the real word? Did you get from the description, that we do not need precise distance to the object (from the sensor), but we only need to detect object inside sensor beam, and result precision for the distance between 2 objects will be the width of the beam or this assumption does not make sense? – Stanislav Jul 01 '20 at 10:10
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    Ultrasonic ranging has the emitter and receiver co-located, seems like maybe you need to take a more careful look at that before your reject it. Start with the cheap Arduino-project ones, but realize that there are better implementations possible. – Chris Stratton Jul 01 '20 at 14:56
  • @ChrisStratton thanks for the suggestion. I checked the specs for these sensors. Looks like the filed of view for each sensor is too big for us. We need to have beam width less than 2 cm in 4 meters distance to the sensor (picture was added to the question) – Stanislav Jul 02 '20 at 09:32
  • That really does not seem consistent with your original question at all - rather it looks like you're constraining the solution in a way the problem does not require, because you've got your thinking stuck on lidar or multiple transverse beams. Firing an ultrasonic pulse down the pipe and timing the echo should work with correct implementation. – Chris Stratton Jul 02 '20 at 14:35
  • @ChrisStratton sorry, I do not completely understand you. Is it clear from the question, that I would like to measure the distance from the object to the static pole, this is not a distance to a sensor. How I can do it with correct implementation for ultrasonic with big FOW? I also would like to emphasize, that pipe in the picture is a virtual tube, this is a just region of interest in the space. – Stanislav Jul 03 '20 at 06:55

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