Counting tyres on a conveyor belt

Hi guys,

Has anyone done anything like this before ?

I am working on a project where I have to count car tyres that are manually placed on a conveyor belt. The belt starts and stops and can also reverse direction so the count must increase in the forward direction and decrease in the reverse direction !

The programming is fairly straight forward, what we are having more of an issue with is the actual sensors themselves.

The tyres might be spaced, but they could also be placed so that they are touching each other which rules out a standard retroflective sensor looking across the belt.

With the belt starting / stopping / reversing having a sensor looking down to detect the "hole" in the centre of the tyre might be tricky to tell the difference between the centre of the tyre or a gap between the tyres.

We settled upon a distance measuring sensor mounted on one side of the conveyor that measures the distance to the tyre - this distance increases and decreases again as the tyre passes through. We then detect the point when the tyre is closest and that is the point we count.

Our first test was with an ultrasonic sensor but the sample rate was not fast enough as the tyres are moving quickly along the belt at 1m/s. We then tried a laser distance sensor and this performed much better, however we are now getting laser "scatter" when the beam hits parts of the thread. This give us dodgy readings and we are struggling to "filter" these out.

So I am looking for some advice or anyone who has done something like this before ?

This needs to be a relatively low cost solution if possible so that rules out any kind of vision systems etc.

Any help with recommended sensors / solutions would be greatly appreciated.

Thank you,

Mark

Aim a sensor at the side of the tire and then count the gaps.

bright676 said:

Aim a sensor at the side of the tire and then count the gaps.

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But they could be placed together so they are touching and there won't be any gaps !

If the distance sensor has an analog output that is what I would use. Since the tires can be touching and you have signal scattering due to treads then it appears to me you are going to have to create either a window (distance range) where you consider it a tire or trend it. What I mean by trend it is as the tire passes the value should climb, reach a max then start dropping (assuming these are round tires). So if you would rather try the trending method you create a table and look for the pulse up to down. Its this going up and coming down that is the key. With the scattering effect you will need to run some type of filer to ignore the scattering effect. For the conveyor reversing you look at the motor starter or VFD to know which way things are running and possible at what speed (speed would effect trending). If it is a motor starter then I would have a timing flag mounted on a idler pulley on the conveyor so I could get a speed reference. Since you know which way the conveyor is running then your trending will work in either direction, just in reverse you want to subtract instead of add. Anyway that's my take on it.

Hi Clay, this is pretty much how we are doing it.

The issue is the analog values coming back from the sensor. The "scattering" from the tread sends these values all over the place and we are finding it impossible to "filter" as they are so random.

Use a whisker switch on the edge of the conveyor it will trip when the edge of a tie hits it, one shot it when the conveyor is moving only. You can get a whisker switch the has two contacts that see the movement backward and forward. You could also use two PEs, looking down, and see the center and the edge knowing whether you see hole or gap. As well if you want to get really technical a vision system would allow you to count only the tire and by conditioning the logic with direction of travel it would add or subtract in the logic.


Something like the one I pasted above is what I have used in the past.

If your laser sensor has only a digital input to the PLC, then use a delay off timer to ensure it doesn't produce multiple inputs to your counter.

lwpowell said:

Use a whisker switch on the edge of the conveyor it will trip when the edge of a tie hits it, one shot it when the conveyor is moving only. You can get a whisker switch the has two contacts that see the movement backward and forward.

Click to expand...

I like the look of this, i'll look into it, thanks.

lwpowell said:

You could also use two PEs, looking down, and see the center and the edge knowing whether you see hole or gap.

Click to expand...

We are considering multiple PECs this could also be a good solution.

danatomega said:

If your laser sensor has only a digital input to the PLC, then use a delay off timer to ensure it doesn't produce multiple inputs to your counter.

Click to expand...

Our sensor only has an analog input to the PLC

Thanks for all the replies, is there a better distance measuring sensor that we could be using ? or are we likely to have similar issues because of the uneven surface of the tyres ?

Are all of the tires the same size?

Can we assume that they all have steel belts in the tread, or not?

If yes and yes, use some side rails to make sure the tires are all in approximately the same position on the conveyor from side to side, then mount a proximity sensor that will see the steel belt in the tire as the closest point of the tread passes by.
If they don't have steel belts, perhaps a capacitive sensor would work in place of a proximity?

No there will be different size tyres, BUT we may be able to fit a side rail to line them all up along one edge.

I think we can assume they will all have steel within their construction although I don't know for certain.

Can we get a sensor with a decent enough range ? I am guessing we would need 50mm maybe ?

I like this solution, another one to look into, thanks !

I think we can assume they will all have steel within their construction although I don't know for certain.

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I thought the belts were stainless steel. Still there are proximity sensors for that too. Baluff has 4 that are good for a 40 mm distance.
http://www.balluff.com/balluff/MUS/en/products/selector-bes.jsp#bes/A_.PDB.PM_M2061.CUR=%3E%2030%20mm,A_.PDB.PM_M2008.CUR=Factor1,

Fargo controls has the X0072 that is good for 50mm for ferrous or 0.9 X 50 = 45 mm for stainless steel.
http://www.fargocontrols.com/extremedistance.html

Omron says these are good for 100mm, either ferrous or non-ferrous.

http://www.ia.omron.com/products/family/479/feature.html

Perhaps a light curtain would work - http://www.bannerengineering.com/en...ing-Array-Sensors/424/A-GAGE-EZ-ARRAY-Series/

Thanks all for the suggestions .....

KB1GNI said:

Omron says these are good for 100mm, either ferrous or non-ferrous.

http://www.ia.omron.com/products/family/479/feature.html

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These look good !

Keyence make some very nice diffuse detection photo sensors with a teach function. You could also try a capacitive prox or, if there is enough steel in your tire, an inductive.