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Multiple Workers Behaving Badly

Creator
Creator

I have a simulation in which there are multiple workers behaving badly.

 

Design:

  • 2 workers in one area of the plant perform either pre1or pre2. These workers share one offloading area to a buffer. (They have different workstations.)
  • 2 workers in a downstream area of the plant perform either Outer or Frame. These workers share no workstations.
  • Each area has a different end-of-shift buffer out of which parts are sorted according to User Defined Attributes.

Problem: Invariably, the simulation run stalls when attempting to move an MU between two different workstations that are not connected. This happens at different times, but always happens on other side of one of the five WIP buffers.

Incorrect move for MU and worker.Incorrect move for MU and worker. .

MUs on exit from WIP shall move to wXF#h, where X is either O or F and # is either 1, 2, or 3.MUs on exit from WIP shall move to wXF#h, where X is either O or F and # is either 1, 2, or 3.

Note: The above figures are from different simulation runs.

 

Attempted solutions:

  1. Change exit controls of WIP buffers
  2. Change exit controls of Prefoam1 and Prefoam2 singleprocs
  3. Change exit controls of end-of-shift buffers - No effect on problem. Returned to previous language.
  4. Change exit strategy from shift end buffers to "Carry Part Away" with additional exit control script to recognize move. No effect on problem. Removed.
  5. Add connectors between workstations on either side of WIP buffer - this creates a complicated and buggy chain of workstation destinations that is not representative of the process.

Any assistance would be greatly appreciated.

 

Thank you!

efk

4 REPLIES

Betreff: Multiple Workers Behaving Badly

Siemens Phenom Siemens Phenom
Siemens Phenom

Hello efk,

 

as you can read in the error message, there is a footpath missing between OD_wip2 and pree11.

I just added this footpath as you will see in the screenshot and the model was running without any error.

 

Hope this helps.

 

Regards

 

GG

 

Betreff: Multiple Workers Behaving Badly

Creator
Creator

That makes the model run, but not according to the correct process. Connecting those two workstations bypasses the buffer. What I can't understand is why the simulation wants the MUs to move from offloading from these WIP (buffer) stations operators to putting the MUs at the buffer infeed.

 

I understood the error message wanting a connector between wOD_wip1 and pre21, for example, but I can't find in the methods and exit controls where that instruction is given.

 

Additionally, with this fix, the offloading worker regularly blocks the onloading worker, and one worker stops working after less than an hour and returns to the worker pool. Indeed, the first Frame (MU) to be completed embarks upon a senseless journey:

Pre:2 should never walk on this footpath and doesn't belong in many of the workstations listed in the next events.Pre:2 should never walk on this footpath and doesn't belong in many of the workstations listed in the next events.

I have tried this fix (#5 in my original post) and it leads to further bad behaviour. 

 

Any ideas on why an MU at buffer offload would want to circle back through that material flow element? This tanks throughput and is not representative of the process.

 

Thank you,

efk

Betreff: Multiple Workers Behaving Badly

Siemens Phenom Siemens Phenom
Siemens Phenom

Hello efk,

 

part SL:43 is carried by worker pre:1 to station OD_wp2.

Buffer OD_wp2 is full so the worker cannot drop the part there and the worker is waiting.

At this point in time, there is a shift event fromobject clock and worker pre:1 carries the part to buffer preShEnd.

The exit control of preShEnd moves part SL:43 to station OD_wp2 without modifying the destination of the part. Therefore when exiting station OD_wp2, the part wants to be carried to pre11 again.

Possible solution:

Alterantive 1: define a new destination for the parts in the exit control of preShEnd

Alternative 2: define 'Carry part away' as exit strategy for preShEnd and set a high priority. After starting the shift again, the worker first will carry away the parts from preShEnd before carrying parts from Prefoam1.

 

Hope this will help.

 

Regards

 

GG

 

Betreff: Multiple Workers Behaving Badly

Creator
Creator
There were multiple stages to solving this problem:

For prePool parts buffer:
1) Keep "Carry Part Away" as exit strategy for "preShEnd" (the buffer)
2) Exit Control SimTalk logic unchanged
3) Add footpaths to/from prePool to prevent workers from using buffer workstation as a shortcut

For WorkerPool parts buffer:
1) Remove "Carry Part Away" as exit strategy for WorkerPool "ShEnd" (the buffer)
2) Add Entrance Control to the buffer to clear MU destination:
"@.Destination := VOID"
3) There are multiple different destinations for MUs, so use exit control to do preliminary sort and move to two new singleprocs
4) Use exit controls in new singleprocs to sort and move MUs to where they belong

I tried to combine 3 and 4 in the latter parts buffer, but it wouldn't work right, and this workaround functions, so I kept them separate.

It seems as though the fewer connectors used directly between workstations, the better (more predictable) the worker behavior will be.

Thanks, GG, for helping troubleshoot and identify error sources.