"Synchronising" product flow on two conveyors

[MichaelG]

For the OP
I have implemented two systems that do this,
One has the product evenly spaced on the conveyor however the phase changes as the machine varies speed (Due to fixed acceleration belts) and the phase change has a transport delay due to the length of the belts. 10 per second using closed loop VSD's.

The other, which may be closer to your system, has the product arriving totally randomly and close together, I have control of three belts where I must accelerate the product to "tray" speed and get the correct phase (position in tray) This is on control logix using servos. (160 units per minute)

Methods - Pretty much as Peter said:
a Gear to lock the axis together, then sensors to detect as the product passes a fixed point, maths to determine what correction move is required, shaped profile correction moves to be as gentle on the product as possible (too rough and the product slips, then your correction move is all out of wack)
For the smartbelts I did use a virtual axis as the infeed master. This axis was then Geared to the "Trays" and I allowed the operators to adjust the phase of this axis for positioning.

 

[markymark31]

Wow, thanks guys, so much information I don't know where to start !

I have tried to show the concept we are looking at on a simple sketch (see link below) :-

http://test.markhammond.co.uk/concept.pdf

There is no actual signal to "drop" the widget onto the trays they will just feed off the end of "smart belt a" on to the tray.

It is my intention to run all the conveyors at the same speed. Our widgets will be fed on to the infeed conveyor at the approximate pitching of the trays so I would anticipate that the "smart belts" would only have some "tweaking" to do rather than major positioning adjustment, but it is critical to hit the trays at the same position each time.

I would like to stick with my CompactLogix if I can so I like the idea of just using VFD's but general opinion in this thread seems to be that servos are the way to go. A servo option looks good but it is something I have not used before.

OkiePC the link to the Kinetix page looks excellent but if I have read this correctly I will need to use a ControlLogix PLC ?

 

[MichaelG]

Nice Picture,
What is the spacing between the trays (approximate)?
What is the spacing between the widgets?

If the Widgets are always being fed at the same rate then VSD's will work.
You would only have to do a small amount of speed matching and phase matching.
Your system will need position feedback for the Tray, the three belts and the incline conveyor (for feed forward). Can you do this on the VSD you are using?

All of the systems that we are talking about are using the mathematics and hardware of the controller to get it to work. Peters RMC70 will easily do it, Control Logix will also do it but will be a little harder. Compact Logix, you could shoe horn it in using kinetics on fiber optics.
Hardware - Hardware capture of position registration mark. (PLC Scan time will NOT be good enough)
As many encoder counts per mm as possible (within the limits of your hardware maximum )

I'll be going to sleep soon and all the guys in the US will add to this

 

[markymark31]

Hi MichaelG,

The trays are around 600mm long, with (approx) a 200mm gap between, so we'll say on a 800mm pitch.

The widgets can vary in size up to a max of 400mm, hence the need for the smart belts so that I can get the leading edge of the widget to hit a predetermined position on each tray.

I have no spec for the VSDs yet so I could choose ones that allow positional feedback.

So are you saying that specialist hardware control is the way to go as trying to do it all within the PLC will be a problem ?

 

[MichaelG]

So are you saying that specialist hardware control is the way to go as trying to do it all within the PLC will be a problem ?

no Just that you need to select the correct PLC hardware eg high speed counter card for encoder with a registration input. - To do it in PLC without the high speed counter or better hardware (eg kinetics) would be a problem

Does anyone know if the PF 755 can do this? haven't had the opportunity to play with one yet.

I think it can with the 20-750-UFB-1 option - sits on Ethernet

What sort of accuracy do you need on the Tray placement +/- 0.1 mm or say +/- 5 mm?

 

[Peter Nachtwey]

What sort of accuracy do you need on the Tray placement +/- 0.1 mm or say +/- 5 mm?

It doesn't look like position accuracy is that critical since a 400mm widget must fall in a 600mm tray. However having high resolution does make it easier to compute accurate velocities for feed forwards but even these demands are not two critical since the down stream speed is fixed and acceleration is 0.

 

[markymark31]

I would have thought tray accuracy + / - 10mm would even be okay, it doesn't have to be that tight.

Is the Powerflex 755 a new drive ? It looks like it might do the job with the optional feedback board ?

 

[Melvin45]

This looks like a great project. In this the synchronization between the two conveyors is very important. I feel it is better to fix the speed of both the conveyors so that the tray is filled properly. Search in the internet to find better solutions. Know more about the working of conveyors then you will get any solution to your problem

 

[paulB]

If you have to use Rockwell product, you may use PowerFlex 700 with build in Compact logix proccessor. This drive in this configuration (with proccessor)become 1.5 axis servo controller. 0.5 axis is feedback only.
PaulB

 

[ELGC]

Hello Peter. How can I watch your video? It is not still available at Delta's website.

 

[Peter Nachtwey]

Peter, can you refresh that link to the video, I missed it yesterday, and the link isn't working for me today.

Thanks,
Paul

https://deltamotion.com/peter/Videos/Auto Lay Up.m4v