Alan Case
Lifetime Supporting Member
Hi, I have a machine that I am designing a control system for and would appreciate any input on the methodology I will be using.
A description of the machine is:
A conveyor belt with 30 diverter flaps spaced along the length of the belt.
At each diverter is an identical packing machine, which receives the product and stacks it into rows and layers, and then delivers it to another conveyor system for wrapping.
I intend to use a micrologix 1200 at each packing machine (approx 30 IO and also 1 high speed counter required)
I also intend to run a device net network using net-dni modules to connect all the 1200s back to a control logix system. (or maybe an SLC505)
The control logix main PLC will take care of the diverters on the main belt(tracking items by an encoder count), messaging to the 1200s the size of the packs required(ie layers and rows), keeping track of the status of each packing machine so that items can be dynamically re-assigned to another packer if the packer is in state where it cannot receive product(this status will also be used further up the food chain for inventory status) and running the outload conveyors and outload wrapping system.
I will paste in some info that Allen Bradley supplied me with on the advantages of a 1756DNB over a 1747SDN. The bit between the stars.
***************************************************************
Both the 1747-SDN and 1756-DNB are comparable as far as
their communication and behavior on DeviceNet. However, the
1756-DNB has more I/O data space available to get the slave
data back into the controller.
For example, the maximum amount of I/O data each direction
in a 1747-SDN is 360 bytes. If you divide this data by your number
of NETDNI modules which is 30, then that means you have a
maximum of 360/30=12 bytes of information that can be transfered
each direction to a NETDNI. The 1756-DNB has 492 bytes of I/O
data which would allow 492/30 = 16 bytes each direction per
NETDNI.
The next major advantage of a 1756-DNB is that the entire 492
bytes of I/O space is brought back as one large discrete I/O
datatable, each direction, every 5 ms. The 1747-SDN has
60 bytes of available discrete I/O data, but the last 300 bytes
of data are M0/M1 data and must be transfered to/from the
1747-SDN using file copy instructions in the user program.
Finally, explicit messaging is much easier to do in the
ControlLogix platform and 1756-DNB, using the built in
message instructions.
*****************************************************************
Can any one there see any problems with the general idea of how this will function. I already have a prototype packer working off an AB ML1200, no problems so far it is just the method of tying it all together and trying to justify the additional cost of a control logix system over an SLC.
Regards Alan Case
A description of the machine is:
A conveyor belt with 30 diverter flaps spaced along the length of the belt.
At each diverter is an identical packing machine, which receives the product and stacks it into rows and layers, and then delivers it to another conveyor system for wrapping.
I intend to use a micrologix 1200 at each packing machine (approx 30 IO and also 1 high speed counter required)
I also intend to run a device net network using net-dni modules to connect all the 1200s back to a control logix system. (or maybe an SLC505)
The control logix main PLC will take care of the diverters on the main belt(tracking items by an encoder count), messaging to the 1200s the size of the packs required(ie layers and rows), keeping track of the status of each packing machine so that items can be dynamically re-assigned to another packer if the packer is in state where it cannot receive product(this status will also be used further up the food chain for inventory status) and running the outload conveyors and outload wrapping system.
I will paste in some info that Allen Bradley supplied me with on the advantages of a 1756DNB over a 1747SDN. The bit between the stars.
***************************************************************
Both the 1747-SDN and 1756-DNB are comparable as far as
their communication and behavior on DeviceNet. However, the
1756-DNB has more I/O data space available to get the slave
data back into the controller.
For example, the maximum amount of I/O data each direction
in a 1747-SDN is 360 bytes. If you divide this data by your number
of NETDNI modules which is 30, then that means you have a
maximum of 360/30=12 bytes of information that can be transfered
each direction to a NETDNI. The 1756-DNB has 492 bytes of I/O
data which would allow 492/30 = 16 bytes each direction per
NETDNI.
The next major advantage of a 1756-DNB is that the entire 492
bytes of I/O space is brought back as one large discrete I/O
datatable, each direction, every 5 ms. The 1747-SDN has
60 bytes of available discrete I/O data, but the last 300 bytes
of data are M0/M1 data and must be transfered to/from the
1747-SDN using file copy instructions in the user program.
Finally, explicit messaging is much easier to do in the
ControlLogix platform and 1756-DNB, using the built in
message instructions.
*****************************************************************
Can any one there see any problems with the general idea of how this will function. I already have a prototype packer working off an AB ML1200, no problems so far it is just the method of tying it all together and trying to justify the additional cost of a control logix system over an SLC.
Regards Alan Case