Waiting time vs Processing time for an object
Accepted solution
Hi @Akshay P,
This is a great question. I don't currently know of any templates that do this within the software, and our resident statistics expert is not in the office today, but here's my best attempt at a solution.
I used an Item Trace Gantt chart, which shows where the flow items are at different times in the simulation and looks like the image below.
This chart creates a standard Statistics Collector with time values we can use to calculate the waiting time and processing time. The only thing that's missing is we don't know which objects represent either "waiting" or "processing." To include this, I simply put a binary label called "timeType" on each of the queues and processors that indicated whether the object was a 0 - "waiting" or 1 - "processing" type object.
Opening up the statistics collector through the tree as shown below, we can add a data tracker on this "object type" label that listens to the event object and checks the label to see if the item just finished waiting or processing.
From the Stats Collector Properties window, we can go to the General tab and click Export Table after a model run to collect all the data in a CSV file.
I couldn't find a good way to aggregate and show this data in FlexSim (I couldn't find a function to calculate the difference in dates), so I took the raw data (shown below) and ran a sql query to aggregate the data to what we need.
The SQL Query I used was the following:
SELECT item, SUM(DATEDIFF(starttime,endtime,"second")) AS timeDiff, objecttype FROM time_type_test GROUP BY item, objecttype ORDER BY item
The results came out to look like this:
As you can see, we now have data that we can work with to see how much time each item spent waiting vs processing. To explain each column:
1) The "item" column is just the number of the item that entered the system in chronological order.
2) The "timeDiff" column is the SUM of the calculated DIFFERENCES between start and finish times GROUPED BY the type of time, whether "waiting time" (=0) or "processing time" (=1).
3) The "objecttype" column tells us whether the object that the flow item entered/exited was a "waiting" type or a "processing" type object.
I know this is a bit of external work to get this data, so hopefully we can find a way to get this within FlexSim, but for now, maybe this will help. Let me know what feedback you have...
Here's the model I used for reference:
Additionally, after throwing the SQL Query result back into Excel and running a simple Find and Replace, the data we get looks like this:
Hi @Akshay P,
Thanks for the feedback. We spent some time digging into the model you've attached and as we were doing so, we noticed that there are a few bugs with the model that might prevent us from getting the statistics you're looking for.
One of the issues doesn't affect the model too much, but it's worth noting: Each of the robots have an On Load trigger that uses items "Type" labels to look up the capacity for that item in a Global Table. There is an item type 3 that is attempting to look at row 3 in the table, but this row doesn't exist. For this reason, you'll need to either bundle the table and look up the value "3" in column 1 or upgrade to FlexSim 19.2 where there's a function called "getValueByKey" that will search the table for the value "Type".
With that resolved, the next issue is that it looks like the Robots are loading and moving some of the items before they have finished processing. We might have to create some kind of buffer that makes sure the items are done processing before a robot is allowed to move the item. I'm not sure if this is really what's happening, so maybe you could explain how the task list is functioning. I've got a screenshot of the task list to help illustrate my question:
At the this time, the Magazine with product_ID "70" is waiting at Oven1 in the 3D model. At the same time, there is a task in the list that is going to attempt to move the Magazine with product_ID "70" (highlighted in red box) from DA2 to Robot1. This means that the Task Executer is going to travel to DA2 but load from Oven1. Am I misinterpreting this or do you think this is something we need to fix? This is happening consistently in the model where the Task List thinks objects are in a different spot than they actually are.
Assuming everything works correctly, I think we can go a different route on setting up statistics. We will assume that Process Flow is synchronized with what's actually going on in the 3D. Then we listen to the creation of the items. Then we will used a tracked variable on the items to indicate when the items are processing (listen for unload at processor and on process finish) and then we'll log the data as "time spent processing / time in model" or something of the like. That way, we'll get accurate statistics based on Process Flow.
For now, let's focus on getting the model to function accurately. If you could help me understand the task list, that would be a great place to start.
Dear @tanner.p,
Thank you so much for your feedback and the indepth analysis of my model. I shall answer both your queries below -
1) Yes, I am aware of that and I will fix it. I actually didn't have the data on the buffer capacities of the robots for the "type 3" product (i.e. a cassette). I forgot that I had labelled it, so thanks for pointing that out. I will fix that issue once I have those numbers and will keep your tip in mind 🙂
2) The second issue was unknown to me, so thanks for pointing that out. I actually included some intermediate buffers in the model as well as my schedule (named "Queue 1" and "Queue 2" in the 3D model. I had also modified my input data to suit that inclusion (as seen here). So the tasks for the product "70" should be executed as follows -
As you have pointed out in your analysis, the product is in Oven1 where as it is supposed to be at the DA1, which should NOT be the case. Can you tell me what could be the exact reason behind this? I am not able to understand why that would happen.
I hope I have informed you sufficiently here. Just to sum it up, according to my 3D model, the products should move in one direction, from one loop to the other (left to right), while stopping at the intermediate queues to wait there until a TE picks it up.
Please let me know if anything is not clear and I will get back to you as soon as possible.
Thanks again for all the help!
Regards,
Akshay Pundir
Hi @Akshay P,
To answer your last question about viewing the active task sequence, you can look at a node in the tree under the Robot called "activetasksequence" as shown here:
As for why the items are in the wrong locations, I think it's a combination of things. The first problem is that the Process Flow doesn't have a way of verifying that a product has been moved or that a process has been completed. What I mean is that if a Robot gets assigned a task of moving an item from Oven1 to Plasma1, it's going to do that immediately based on the Process Flow, even if it's supposed to wait until a certain time or event in the future.
In addition to that, the table is set up such that different robots are handling the same items at different times. In the case of our Magazine item with product_ID "70", Robot1 is going to unload the Magazine item at DA2.
Meanwhile, Robot2 is going to load the Magazine item from Queue1 (it's not there, but it will steal it from Robot1) and unload it at Oven1.
These screenshots were taken from the same model time. It might be a problem with the table of tasks not executing like you'd want it to. To be honest, this is more micro-managing than I would typically see or recommend in a FlexSim model. Have you considered eliminating the Robot assignment and then using triggers instead to determine which tasks to send to? For example, instead of telling Robot2 to move Magazine item 70 from Queue1 to Oven1, maybe you could have a trigger associated with the Queue that looks up in the table what the next process is and then acquires an available AGV and sends the item there. You could even have it try to acquire a specific AGV.
By doing your logic this way, the AGVs aren't going to override the processing and waiting times in your 3D. There are some instances we noticed that the items appeared to be mid-process when an AGV came along and picked them up to move them. I think we could achieve more accurate statistics going a different route. What do you think?
Once we've got those things sorted out, I'm wondering how you'd like the wait time and processing time measured. Would an average wait and processing times for all flow items work? Like an average? (i.e. 25% waiting, 75% processing) Or would you prefer to have each item's specific wait and processing times? (i.e. Item1 - Waiting: 300 seconds; Processing: 900 seconds)
