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I want to try measuring the orientation of an object by measuring the distance between a "flat" surface to the surface of the rotated object. The problem I assume is that if the surface being measured is at an angle to the distance sensors, the beamed lights from laser or infrared proximity sensors, for example, would be reflected at an angle and not return to the sensors at all. enter image description here Would this actually happen, or am I misunderstanding some properties of these sensors? Which sensors would work in this kind of application, and which sensors would not work for sure (I read from another post that ultrasonic sensors would definitely not work in this case)?

(Added a crude sketch of the problem I think is going to happen)

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  • What type of surface does the object have? Is it rough or reflective?
    – chrisl
    May 13, 2021 at 14:03
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    I'm looking to try to measure the orientation of a truck-trailer surface, so I imagine it would be a smooth surface of painted sheet metal. I'm not sure how reflective this would be considered, but something like: ryder.com/used-trucks/-/media/Project/UsedTrucks/UVS/Images/…
    – Eric
    May 13, 2021 at 14:07
  • You can try a TOF (time of flight) laser distance sensor. That normally works, when the surface is not too reflecting for the laser light
    – chrisl
    May 13, 2021 at 14:34
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    A laser distance sensor will work when the surface is not like a mirror. The more power you use the better the sensor will work (but be careful about laser safety). An ultrasonic sensor on the other hand is less affected by the reflectivity of the surface, but sees a very wide signal if the surface is not perpendicular. This probably won't give you usable measurements.
    – PMF
    May 13, 2021 at 18:06
  • Honestly, I don't think anyone here can give you a definitive answer. The results depend on many variables in your whole application setup. I would suggest just testing it. For this the only really viable options (besides some mechanical solution) are ultrasonic or laser TOF. I would start with ultrasonic, since these are really cheap. If you don't get good results with them, try a TOF sensor.
    – chrisl
    May 14, 2021 at 9:08

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Using ultrasonic sensors would be a very sensible solution in your use case.

I am currently working on a similar project with a company in Denmark, where the objective is to detect cars on parking spaces. For this task, I used two of these ultrasonic sensors from DFRobot for the prototype:

https://www.dfrobot.com/product-1935.html

They were very easy and simple to setup on an Arduino UNO and worked perfectly fine even when two were sensing at once. Though I have to mention, that they need a serial connection each, but this can be worked around using a multiplexer or a developer board with more serial connections.

I also found that the ultrasonic sensors work better than time of flight sensors in outdoor conditions. They are very robust and wont be as affected by dirt for instance. A little speck on the lens of a ToF sensor and it will be rendered useless.

Ultrasonic sensors are also widely used in the car industry for parking aid solutions where they have to detect lots of different surfaces and be very precise in doing so.

Ultrasonic sensors are great. And yes, they can interfere with each other, but as long as you dont put them on top of one another, it should not be an issue.

You should be able to detect the distance to a trailer in two different places using ultrasonic sensors as long as the trailer is within the sensors range.

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  • Hey, thanks for the response! I've read online that ultrasonic sensors don't work with angled surfaces (around 5 degrees off perpendicular). What has been your experience with this? Would the readings give completely wrong numbers, or simply numbers that are close, but with a larger margin of error? Or has this not been a problem at all in your experience? Thanks!
    – Eric
    May 14, 2021 at 13:17
  • It will depend on what sensors you'll choose. You can easily find sensors with more play than 5 degrees. I found that the one i linked will work until around 12-14 degrees, but if this is not enough, you could perhaps use two sensors attached to stepper motors at each of the trailer and let them spin around sensing at different angles. Alternatively, you could construct some kind of parabolic array. This will require a few more sensor though.
    – BatS00p
    May 14, 2021 at 15:36

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