Sensor to detect plastic film, edge detection

[MyMack]

Hello,  Could someone please recommend a TOF sensor(or other) for reliable plastic sheet detection.

Application: Measure the width of a sheet or film of plastic in production environment.  We would use  two sensors to detect the edges of the film.  We would move the sensors in/out on a carriage mechanism until the edge is detected. Continuous measurement,  plastic film would be passing by the sensor(s).

              Sensors to be mounted between 5 and 20mm from target, plastic film.

               Sensors must be able to detect all types of plastic, from clear or transparent (eg. Cling film) to black (bin liners)  IR light source?

              Sensors must detect presence or absence of plastic film so that edge can be known.  Carriage movement then gives width.

Want to measure width of film with precision of 1mm or better.

 

I have looked at VL53L4CD for example.  Would this work?  Also looked at the demo video with the 53L0x, but distance range most likely tooo long. Can you recommend a different or better TOF sensor for this application please?

Michael.

[Ozone]

>  Would this work? 

I would think, no.
A TOF sensor is based upon the reflection of a signal from the surface. I can see no dependance from thickness there.

As a side note, I know e.g. that paper machines measure the thickness of the paper running through with radio-activity. Attenuation is proportional to thickness (everything else being equal).

Since you talk about different materials with different characteristics, you might need something similiar.

[Andrew Neil]

I think @MyMack is talking about the width of the sheet - not its thickness?

[MyMack]

Thanks Andrew for pointing out my mistake.  Yes,  I meant width,  we want to measure the widtth of the plastic film.

[Ozone]

Ah yes, sorry.

Still, I can't see how you would want to measure a dimension rectangular to the axis the sensor's working principle is based upon.
Scanning like LIDAR, perhaps.

Multipe light barrier sensors ?

A machine vision solution ?

[MyMack]

Ozone,   we would be measuring the side-to-side width by moving two sensors on a scanner type system.   Each sensor would need to track the film edge.   Scanner movement or displacement then give the width.

[Andrew Neil]

Maybe a pneumatic solution: the edge of the sheet either covers or doesn't cover a small hole - thus allowing air to escape or not ?

Use a pressure sensor to detect when the hole is covered or not

[MyMack]

Andrew,  that is an interesting idea,  never thought of it before.   Would be concerned though that an air bleed might damage some of the plastics.   IR sensors are used in industry for this purpose.  And we have used a home made IR retro-reflective sensor previously.   I want to find something that takes care of the processing part of the received signal,  hece looking for an off-the-shelf TOF sensor or similar.

[Andrew Neil]

shouldn't need to be high pressure

[MyMack]

Andrew,   can you point me to some resources,  sensors etc,  as to home such a system might work  It mus be non-contact,  it would not be acceptable for the nozzle to touch the plastic.

[Andrew Neil]

---

@MyMack wrote:

it would not be acceptable for the nozzle to touch the plastic.

---

isn't the plastic already running over rollers/bars?

[MyMack]

Yes,  the plastic is running over rollers. But there is a difference between that and an air nozzle traversing across the film,  where there might be the possibility of tearing or scratching.   But on second thoughts,  perhaps the nozzle could be built into some form of plate that the plastic could roll across. It is a new concept for me.   I am trying to think what air pressure,  and what pressure sensors could be used.  And what precision (mm) edge detection could be achieved.

[Andrew Neil]

I didn't suggest a nozzle. I said a bar with a hole in it - something like this:

 

http://www.decodesystems.com/ce-punched-readers.html#:~:text=have%20been%20omitted.-,AIR%20SENSING,-1.%20An

(that shows vacuum; I suggested pressure)

 

Instead of detecting a  hole in the material, you're looking for the edge of the material

As you can see from the article - it's actually a very old concept!