OT: Volume Sensing

Brijm · May 9, 2012

I recently did some automation on a mulch coloring machine. One of the final things, to make this machine fully automatic, is to sense the yards of material (ground wood chips) processed through the machine. We are currently counting the wood being dumped into the machine from the front end loader, which is not very accurate to control to.

My only thought to detect the volume of material being processed, is to use a laser or other sensor to measure the height on the v-belt exiting the machine. Assuming a constant belt speed, I could somewhat accurately calculate the volume.

With the cost, to try this, I don't have a lot of confidence that this will work. Does anyone have experience measureing something similar?

Clay B. · May 9, 2012

Generally the most accurate way to do this is through weight measurement. Basically dump material into a bin weight the bin then discharge the bin. This would be your most accurate. Since your product density is going to vary due to the irregular shapes and sizes you will always have a volume error.

It really depends on how precise you want to be. I would find out what kind of error you can have. That more than anything will dictate how you need to measure this.

Brijm · May 9, 2012

Thanks,
But I don't think that weighing will work, as the weight will vary with the moisture content. Also, I can't dump a large load onto the belt.

A quick review of the process. They use a bucket loader to load wood chips into a grinder hopper. The ground material is fed by belt into the coloring machine hopper. Both the coloring machine hopper, and the grinder can vary in speed. Color and water are added to the wood, and then discharged onto a v-belt, which carries the end product to the correct pile. They are processing up to about 200 yards of material an hour, and from 40-80 gpm of water.

The material needs to flow through the system, so I can't really stop it anywhere.

shawn_75 · May 9, 2012

Use a color sensor and achieve consistent results no matter the volume or moisture content.

http://www.pepperl-fuchs.com/global/en/classid_49.htm

Just a thought.

nonuke · May 10, 2012

The way it is done in some paper mills that I know, is to dump the wood into a water tank with a known water level, and measure the displacement of water in the tank after the wood is dumped. The wood is submerged completly in the water with the help of a dumper.

bce123 · May 10, 2012

as the weight will vary with the moisture content

no answers yet just questions. would not the moisture content and type of wood need to be known to determine soak time as dry soft would absorb much more dye than wet hard wood?

James Mcquade · May 10, 2012

from my viewpoint, moisture is not an issue.
you need to know the yards of materials being processed.

as the material is being transported to the coloring system, use ultrasonic sensors to measure the product height. compute the average and derive a formula.
i use an omron line scan laser for a similar type of operation on a much smaller scale with good results.

regards,
james

OkiePC · May 10, 2012

Our IFM Efector rep. recently bragged about this sensor:

http://www.ifm.com/ifmus/web/news/pnews_8r3n6b.html

We plan to try them to detect volumes in hoppers on equipment unsuitable for load cells. According to the rep. they're easy to set up...you teach zero to tune out background equipment, and they prove a 4-20mA output for easy interface to a PLC.

You might be able to use something like this on a moving belt and take snapshots at regular intervals, or in conjunction with load cell on one of the hoppers in order to determine the relative density of the material.

Brijm · May 11, 2012

Thank, you for the help.

The IMF sensor looks very promising, although I'm curious as to the price tag. James was thinking along the same lines as I was, although I'm not convinced yet on the accuracy there.

I also asked a buddy who is a mechanical eng. He had mentioned a paddle wheel type design, between the mulch machine, and the discharge conveyor. This might be a consideration as well.

OkiePC · May 11, 2012

Brijm said:
The [IFM] sensor looks very promising, although I'm curious as to the price tag.

Retail $1450:

http://www.ifm.com/products/us/ds/O3D200.htm

Lancie1 · May 12, 2012

I also asked a buddy who is a mechanical eng. He had mentioned a paddle wheel type design, between the mulch machine, and the discharge conveyor.

That idea is about what you would expect from a HVAC engineer. The old Bindicator paddle-wheel level switches were not very good even for sensing a set level in a bin (Low or High Level Switches). I don't think they would work at all to indicate a variable level on a moving belt. Maybe he was talking about some other type of paddle wheel switch.

leitmotif · May 12, 2012

Brijm said:
I recently did some automation on a mulch coloring machine. One of the final things, to make this machine fully automatic, is to sense the yards of material (ground wood chips) processed through the machine. We are currently counting the wood being dumped into the machine from the front end loader, which is not very accurate to control to.

My only thought to detect the volume of material being processed, is to use a laser or other sensor to measure the height on the v-belt exiting the machine. Assuming a constant belt speed, I could somewhat accurately calculate the volume.

With the cost, to try this, I don't have a lot of confidence that this will work. Does anyone have experience measureing something similar?

This strikes me as a lot of challenges. You are dealing with ground up wood. I assume you have mixed species, different levels of moisture content when ground and the list goes on.

I think that no matter how many controls and measurements you put in place the final measurement will be done with
Mark I Mod 2 human eyeball. Factor in that beauty is in the eye of the beholder (the guy buying the stuff) and you have all sorts of variation.

Maybe measuring the color of sprayed material is the way to go.

Dan Bentler

Brijm · May 13, 2012

Lancie1 said:
That idea is about what you would expect from a HVAC engineer. The old Bindicator paddle-wheel level switches were not very good even for sensing a set level in a bin (Low or High Level Switches). I don't think they would work at all to indicate a variable level on a moving belt. Maybe he was talking about some other type of paddle wheel switch.

Think more of a volumetric flow sensor. The faster the flow, the faster the paddle turns.

Brijm · May 13, 2012

leitmotif said:
This strikes me as a lot of challenges. You are dealing with ground up wood. I assume you have mixed species, different levels of moisture content when ground and the list goes on.

I think that no matter how many controls and measurements you put in place the final measurement will be done with
Mark I Mod 2 human eyeball. Factor in that beauty is in the eye of the beholder (the guy buying the stuff) and you have all sorts of variation.

Maybe measuring the color of sprayed material is the way to go.

Dan Bentler

Dan,
Unfortunately to my understanding, spraying too much color, won't change the color of the product, but will significantly change the cost of operation. Also, it is possible to spray too little dye,and have a product that looks good initially, but fades quickly. Not ideal for control.

Peanutz · May 13, 2012

Weigh Belt Feeder

It is quite a common practice to weigh material on a moving belt, typically cut out a section of the conveyor's frame work and introduce the mechanically isolated scale. Allow the belt to make contact with this section which is fixed to load cells, a stand alone peripheral device will give you 4 - 20 mA, put that into your PLC and scale it as you wish and integrate it into your code. Yes, yes before anyone says it you could contition your load cells and use an analog card directly into your PLC.

OT: Volume Sensing

Brijm

Lifetime Supporting Member

Clay B.

Lifetime Supporting Member

Brijm

Lifetime Supporting Member

shawn_75

Member

nonuke

Member

bce123

Lifetime Supporting Member

James Mcquade

Member

OkiePC

Lifetime Supporting Member

Brijm

Lifetime Supporting Member

OkiePC

Lifetime Supporting Member

Lancie1

Lifetime Supporting Member

leitmotif

Member

Brijm

Lifetime Supporting Member

Brijm

Lifetime Supporting Member

Peanutz

Member

Similar Topics