Is it possible to increase multi-target distance resolution on VL53L3CX?

[GHuan.2]

Hi ST team, I"m developing an application of proximity sensors on a robot with VL53L3CX. The robot moves not very fast and we have already implemented proximity sensors with  VL53L0X on it. Now we want to add multi-target capabilities with L3CX chip.

The problem is we want higher multi-target distance resolution with the new sensor. With some experiments we found the min detected separation between objects/targets is around 70cm, and as I found in previous questions/posts you only formally support 80cm separation/resolution.  If we don't need long range, for example if 80cm to 100cm is the max range, is it possbile to customize a driver to support higher multi-target/object distance resolution for our application?

Thanks in advance.

[John E KVAM · Accepted solution]

the sensors work by emitting a train of 2 nano-second pulses and then collecting the number of photon strikes per clock. Each clock is one bin of a histogram. There are about 4 bins in that 2micro second period. 

For that reason, the two targets have to be separated by 80cm. It's the length of the VCSEL (Laser) pulse.
If the two targets are closer together in depth, the histogram does not show two distinct 'lumps', but one sort of elongated shape. 

From this shape we can warn you that the target is 'complex'. We call it a merged target. But we really cannot tell you more about where the second target really is. 

 the solution is the VL53L8. It has a faster clock, meaning the targets can be a bit closer together - 60cm. But what it has is an 8x8 grid of zones - each 5 degrees square. I'm betting that any second target will show up in an adjacent zone. 

Unfortunately, the VL53L8 is more expensive. But it will solve your issue.

- john 

[GHuan.2]

John, thank you for your professional and quick response. We really need the multi-zone feature in the future, but our robots works outdoor, with VL53L0X basically we have mitigated sunlight interference, but with a wider open window on sensors, it will be more challenging. And our product price could not be very high. So if sunlight is a problem, we'll still looking for solutions with single-zone ToF sensors currently.

[GHuan.2]

Hi John,  'a train of 2micro second pulses' has typo right? if it's 2 nano second, then the distance between adjacent photon  lots is 60cm?

[John E KVAM]

I hate it when that happens. you are correct of course.

Apparently, I cannot type and think at the same time. 

- john

[GHuan.2]

Hi John, our application with ToF sensors is a window/glass cleanin robot. we want to distinguish cover window smudge from window frames, or frame from nearby wall. the robot moves not very fast. As you said, multi-zone tof sensors may be a solution. But it should be able to overcome signal saturation problem caused by sunlight when it works on outside of glass. I'm not sure tof with wider fov is ok, and we need to consider the price.

if the design with single zone will not change in short time, we'll still use single-target sensors for some time. and I'll close this issue. Thanks.