Weight measurement of a moving conveyor

Hi,

I have a conveyor belt that gets loaded with packages at a variable rate. All i need to determine is the total weight passing on the conveyor based as the person loads it at one end. I am considering adding a small separate conveyor at the end whereby a single package drops on to this conveyor that has a load cell underneath it. I then average 3 or 4 readings as the packed moves over this then drops off the end. This is the weight of the first package only, then the following packages each do the same. Note that the conveyor cannot be stopped nor its speed changed.

I bought the Sparkfun 50kg load cell for this. The maximum weight would not be exceeded and the accuracy of 0.5kg is ok. https://www.sparkfun.com/products/10245

Questions:

• Is there a simpler way and can i do it with the principal conveyor only?
• Can i somehow record the single package weights (the 3 to 4 averaged values) and the total accumulative separately. There would be a period where the conveyor does not have a package on it, so this dead weight should not be processed

Any help greatly appreciated. Please let me know if more details are required.

If you can arrange the packages so that at most one of them is on your short belt at a time, that could be made to work. The only other approach that makes sense to me would be to support the main conveyor (or a section of it) so that all the weight of one end was carried by a weighing device. Then you could look for a sudden increase in weight as each new package is placed on it - the peak would tell you the weight of the new package, and you would expect that weight to reduce progressively as the package moves from the weighing end to the non-weighing end. I suppose you could put the scales at the far end and look for weight suddenly being removed, instead.

Your separate conveyor is all I can think of, itâ€™s length would have to be < the distance between packages, is that feasible?

Are all the packages the same size, just different mass?

Rob

I previously thought about raising one end of the conveyor, but its mass is far too much for the load cell i have. Granted i could get a bigger one, but the main conveyor weighs almost a ton. The other problem with suspending the main conveyor is vibration which will affect the measurement (due to the motor size required to move the belt on the idlers).

The separation between the packages could be made sufficient to prevent two packages being placed on the separate conveyor at any one time. The packages are different sizes, shapes and of course mass.

Your "separate conveyor" doesn't really have to be a conveyor eh? The package can drop onto a weighing plate, then be pushed off with an actuator or by tilting the plate. Where it goes after that I have no idea, onto another conveyor, into a bin or wherever it goes now.

Rob

Can you post a picture of the situation?

Why can't you weigh the stuff where it's being loaded?

What about before it goes on the conveyor? Perhaps when the boxes are packed?

Bump.... any new ideas with this one? I'm still banging my head against a wall. Thanks.

burt46: Bump.... any new ideas with this one? I'm still banging my head against a wall. Thanks.

That often happens when you go joy-riding on a conveyor belt.

The obvious solution is that you mount a number of rollers (at least two) spanning a given absolutely level section of the belt, on strain sensors. Given that the spacing between packages is such that only one will be on that section at any given time, you can digitally total the results of the sensors. You record the peak (plateau) measurement as the item passes.

You are of course always going to get some error weighing through the belt.

Obviously you figure out the passage time on the belt to calculate which objects are on it at a given time.

Although that might be the obvious solution, and in fact how many industrial application work (albeit with better precision and cost), how can i attach a Arduino based load cell to idlers and expect to get a reliable reading? Idlers distribute weight which can vary on either side of the spindle. So i would need cells on either side of each idler and try and write code that can compute the overall weight of the package based on a minimum of four load cells and then spit out a single number? Is this what you had in mind? Doable i guess for a flat conveyor, but mine has side rollers to prevent anything falling off. Therefore i'd need a minimum of 12 load cells to do this. :fearful:

burt46: and in fact how many industrial application work

I would have thought so.

burt46: So i would need cells on either side of each idler and try and write code that can compute the overall weight of the package based on a minimum of four load cells and then spit out a single number? Is this what you had in mind?

Dead easy way to do it. Noted that most "electronic" personal ("bathroom") scales now have load sensors in each of four feet and total the readings (probably as an analog addition prior to the ADC). Much more reliable than mechanical linkages. You can either do this (op-amp as an adder) or feed them into ADC channels (or use an external multiplexer - the Arduino of course has an internal multiplexer and one ADC) and add them up - exactly what microprocessors are so good at.

burt46: Doable I guess for a flat conveyor, but mine has side rollers to prevent anything falling off. Therefore i'd need a minimum of 12 load cells to do this.

If you mean slanted rollers, that could be tricky. Vertical rollers would not count.

I should imagine you would attach all rollers in a set to a single support bar and have one load cell under each end. A (pair of) long radius bar(s) parallel to the belt would stabilise it.