Random Ranging Distance irrespective of target presence

[Akansha]

Hi,

I am working on VL53L1CB sensor for designing Obstacle detection sensor.

I have tested with accuracy and range of sensor.

I am encountering the problem of random ranging when there is no target in front of sensor.

I kept the sensor at height of 15cm from base and there is not obstacle in front of it within FOV of 27 degree. Still, it is showing ranging distance varying from 850cm to 1200cm sometimes.

I am not getting weather this is the case of ground detection or there is any other reason.

Please assist me dealing with this

Regards

Akansha

[ACHOU.18]

​Hi Akansha,

Firstly, We would like to know your test setup because without target you are getting ranging result is quite weird. In addition, pls provide following points:

1. What is the range status when you get result (850-1200)cm instead of 15cm ?  How do you see the result ? FYI,  our ranging results are in mm.
2. Does the sensor have a Cover glass ?
3. Pls send us the log file with range status, distance, signal rate, ambient rate.
4. what is the material of your ground ?

Regards,

Aditya

[Akansha]

Hi ,

I am attaching test setup of sensor. I kept the sensor at the height of 10 cm from ground and obstacle were placed in front of the sensor over flex sheet.

1. I meant that sensor was placed at the height of 15 cm from ground and there was no obstacle in front of it, Still it was giving the ranging distance in range of (850 - 1200)mm. By mistake i have mentioned the unit cm.
2. No, Sensor doesn't have any cover glass while testing.
3. I am attaching log file for your reference.
4. Sensor was placed on the flex sheet (PVC material). Snapshot of test setup is attached below.

 

Log File

Regards

Akansha

[ACHOU.18]

​1.I meant that sensor was placed at the height of 15 cm from ground and there was no obstacle in front of it, Still it was giving the ranging distance in range of (850 - 1200)mm. By mistake i have mentioned the unit cm.

Ans: Pls do offset correction (refer to UM) and try ranging. It seems to me ground is not even.

In addition,  we developed a very light code footprint for such kind of access control Mass market application. If you are not interested in multi object detection , you can checkout ULD API which is much easier to integrate  (https://www.st.com/en/embedded-software/stsw-img009.html ) and play around .

you consider only ranging status =0, follow the similar type of code:

status = VL53L1_GetRangingMeasurementData(Dev, &RangingData);

if(status==0){

       printf( take into account range parameters for further action);

}

[Akansha]

Hello,

I have gone through the offset calibration procedure. As per manual grey target needs to be placed at 140 mm from sensor in dark environment.

So i am having doubt that if i will calibrate sensor in dark (no infrared) environment then how sensor will work correctly in normal warehouse environment?

Calibration function preferable for Ranging Mode is VL53L1_PerformOffsetPerVCSELCalibration(Dev,CalDistanceMilliMeter), Do i need to put CalDistanceMilliMeter = 140 mm as per calibration procedure?

As per manual, Calibration results are:

• algo__part_to_part_range_offset_mm

• mm_config__inner_offset_mm

• mm_config__outer_offset_mm

Without performing any calibration i checked these parameters and got their value (0, 51, 21).

So i am having doubt whether i need to set these after performing calibration or these parameters will get automatically set?

And what is the significance of these parameters?

Please help me resolving above mentioned queries.

Regards

Akansha

[ACHOU.18]

​Hi,

Yes, Calibration procedure is done in Dark environment where no ambient light is affecting return signal rate. Moreover, user need to store the mentioned parameters in NVM  and apply those parameters  before datainit and static init function. You do this step one time, then you need to  load those offset parameters instead of doing repetitive calibration. These parameters are used by internal algorithm to offset the error in distance.

Regards,

Aditya

[Akansha]

Hello,

Thanks for the reply!

It would be really helpful if you will list down the steps required in offset calibration and significance of above mentioned parameters.

Does this offset calibration will increase the range of sensor?

Regards,

Akansha

[John E KVAM]

The calibration does not affect the range, it affects the accuracy of the range.

But I think I see a flaw in your experiment.

If you take a piece of paper and fold in diagonally you get a 45 degree wedge. Fold it again and you will get 22.5 degrees. Then place it in front of your sensor. This will give you a very rough idea of what is in your Field of View (FoV).

A 27 degree FoV has a diameter of about half the distance.

So at 30cm the FoV is now 15cm in diameter. At 60cm the Fov is 30cm in diameter.

if you sensor is 15cm above the floor, you will start to see the floor.

and you will start to see a return signal from the floor after that.

using the piece of paper as a guide slightly tilt your sensor upwords. At some point you will no longer see the floor.

In my 2D lidar video https://youtu.be/BMR-IPMGJSE I use this approach.

The video uses the VL53L1X, but the video shows the slight upward tilt you are going to need.

• john