TOF Sensor Feasibility

[jesse-TP]

Hello,

We are researching the feasibility of a new product and have some questions regarding STMicro's TOF sensors. At this time we are narrowing on the VL53L4CX, but I am sure these questions apply to most of these sensors. 

The product is detecting distance of a flat, white, square coupon normal to the sensing field. About three inches by three inches. 

The questions are as follows:

1. It seems like ambient light has the most dramatic effect on range of the device. Does it also dramatically effect measurement repeatability and accuracy? As a result, are these sensors generally not used outdoors? Is there a way to compensate for the effect of ambient light?

2. The size of the full visual field for these sensors, even with a 18 degree FOV, gets pretty large past several feet. Is there an understanding of how much of the visual field an object needs to take up for it to be detected? For instance, can a 3inch by 3 inch test coupon be detected at 3 meters, neglecting the effect of ambient light?

3. Repeatability is very important for our application. What aspects affect repeatability? I have read some of these sensors can reach a repeatability of 0.15%. What kind of actions or environment need to occur for this level of repeatability to be possible?

Lastly, if we prize accuracy, repeatability, and reduction in the effects of ambient light above all else (with at least 3 meters of range), is there another TOF sensor you would recommend, or another technology?

Thanks!

Jesse

[John E KVAM · Accepted solution]

Is there a way to compensate for the effect of ambient light?

Ambient light is a huge issue. The sensor measures the ambient, then looks for a signal above that ambient. But sunlight is a massive interferer and definitely limit the distance of the max range. Unfortunately, the only thing you can do is avoid the sun. 

Can a 3inch by 3 inch test coupon be detected at 3 meters?

The FoV at 18 degrees means the diameter of the circle of light is about 1/3 the distance. So at 3M you are covering an area 1 M in diameter. 

The sensor would like 20M photons/second. The sensor can work down to about 0.5M photons per second. 

The only way to get that many photons is to make your coupon out of retro-reflective material. (Think safety vests.)

But without a mirror or the retro-reflective material 3x3 is out of the question.

 Is there another TOF sensor you would recommend, or another technology?

The Bosch Laser range finder is what you want. Works the same way but with a focused visible laser. Unfortunately, the cheapest one is $50 at Amazon.

One cannot focus our invisible laser. The resulting light would be very dangerous.

[jesse-TP]

Thanks John, this is very helpful information.