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March 9, 2021
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ToF sensor to detect presence, speed and orientation of moving object? VL53L1CB or VL53L3Cx

  • March 9, 2021
  • 1 reply
  • 1250 views

Hello, I like to consult the community if the latest ToF sensor can be an option for my application. As depicted in the image, a stream of box-like objects moves along a conveyor-like system where each "section" of the conveyor may deliver different speed. The goal is to be able to constantly detect and closely monitoring the (1) object presence, (2) linear speed and optionally the (3) orientation, of each object throughout the moving process.

Since we're expecting hundreds of sensors to be installed per line, and that we are restricted by the already confined space, the price point and form factor of ToF sensor seems to be a good fit.

Digging through the datasheet, it looks to me that VL53L3CX might be the better choice (the flyer states ""fast accurate distance ranging and short distance linearity) and 50-60Hz should be sufficient to calculate a rough orientation. It's more now of my concern on how well a pair of VL53L3CX can detect moving speed. Or is there a way to determine (or estimate) a theoretical precision of speed measurement.

Comment and suggestion is welcome.

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    Best answer by John E KVAM

    this is a difficult problem. The ToF sensor sends out light in a 27 degree cone and returns the average distance all the photons travelled. So you are only going to get one point. If your box it turned as in the leftmost orentation you will get a large number, then a shorter one as the edge crosses then progressively larger numbers at the back of the box. Then you will get a distance to whatever is beyond the box.

    In the case of the vertically orentated box you will get a consistent distance as the short side moves past.

    The third box will look a lot like the first one, but the durations will be different.

    And the fourth will look like the second - but the duration will be longer.

    The VL53L1CB has the ability to narrow the field of view. That might work well for you. And it has the ability to change zones between ranges. So you can look to the left, then center, then right. You might find value in that.

    1 reply

    J
    John E KVAMAnswer
    ST Employee
    August 19, 2021

    this is a difficult problem. The ToF sensor sends out light in a 27 degree cone and returns the average distance all the photons travelled. So you are only going to get one point. If your box it turned as in the leftmost orentation you will get a large number, then a shorter one as the edge crosses then progressively larger numbers at the back of the box. Then you will get a distance to whatever is beyond the box.

    In the case of the vertically orentated box you will get a consistent distance as the short side moves past.

    The third box will look a lot like the first one, but the durations will be different.

    And the fourth will look like the second - but the duration will be longer.

    The VL53L1CB has the ability to narrow the field of view. That might work well for you. And it has the ability to change zones between ranges. So you can look to the left, then center, then right. You might find value in that.

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