Delayed Events

[john.b...@arup.com]

Hello,

I wonder if anyone has found a nice way to achieve the following use case.

I have an EntityConveyor which has, say, a travel time of 10 s. In order to control other parts of the model I'd like to have an indication of when an Entity is in the last 2 seconds of the conveyor. I want to use this to control/define an ExpressionThreshold: it's "open" if there is no item on the conveyor in the last 2 seconds of travel time; "closed" otherwise.

I can write little expressions to capture the entry time of an entity when it enters the conveyor and to calculate +8 and +10 seconds to define the window of interest and save these as attributes for each entity on the conveyor. I can also use the EntityList of the conveyor to find the first entity and hence the next +8 and +10 s times to use. These can be put into an ExpressionThreshold to see if SimTime is between these two limits and so set open or close. But, as the user manual makes clear, these states only get updated when events happen. So, it is not a robust approach.

Is there another approach that would work that I have missed, or could there be a need for a type of "delay object" that is used to schedule an event/update in the future based on a current event?

My current try at a workaround is to generate loads of events but this is bad for performance and intellectually quite "wrong"!

Best wishes,

John

[john.b...@arup.com]

I have modified EntityConveyor.java which now allows a new input of X time before reaching end of conveyor to be set and a new Boolean output which is TRUE or FALSE depending on whether or not there are any entities within X time of reaching the end of the conveyor. This also creates an event when an entity will reach this end zone so that anything watching/connected to the conveyor (e.g. an ExpressionThreshold) will respond to this happening. I have run a few basic tests and it seems to work as intended. Shared for info in case anyone finds this useful. (In my case, it is handy to know when an entity is near the end of a conveyor to give it priority over a merging conveyor input when entering the next conveyor - see attached model which uses the new input/output - see screenshots.)

[john.b...@arup.com]

I have now "reversed" the logic so that it matches ReadyForNextEntity. As a result, the new output is called "NoEntityApproaching" which returns TRUE if no entities on the conveyor are within their exit proximity time of leaving the conveyor. When linked to a ExpressionThreshold it feels a bit more natural so that TRUE/GREEN means that a downstream element can be released without conflict/contention. New version attached here.

[Harry King]

Hi John,

Why not just represent the conveyor by two EntityConveyors: the first with a delay of 8 seconds, and the second with a delay of 2 seconds?

Harry

[john.b...@arup.com]

Hi Harry,

For sure, I could use two conveyors as you suggest (indeed I have done that in the past), but it's partly a question of convenience and partly clarity/mapping to "real" equipment. I'm always looking at baggage conveyor systems, and I do have an aspiration to have modelling elements that have a (closer) one-to-one relationship with those physical conveyors and their controls. Thus, the ability to have accumulating and non-accumulating EntityConveyors that you developed is really good. In contrast, the positioning of where entities stop has been tricky (understandably) when they "hang over the end" of an EntityConveyor - though recent changes to alignment options I think have helped. In non-trivial systems there is also a lot of "wiring up" of ExpressionThresholds to mirror the controls. Maybe this is taking the basic JaamSim to a place that isn't of wider interest, and we should be grateful (and look, I and others are _hugely_ grateful) for the ability to model behaviors through constructs made up of the basic functions (e.g. your two-conveyor suggestion). Perhaps there would be a palette of "conveyor" objects that's part of an extended version (a bit like your Pro version)? It feels tantalisingly close to be able to use JaamSim to go from laying out a concept to animation/visualisation (in my field). Anyhow, your time is precious, and I quite understand that priorities could lie elsewhere!

John

[Harry King]

Hi John,

I've been thinking about your desire to trigger an event when an object reaches a specified position part way along the conveyor. This seems like a generic problem for discrete event simulation. Normally, there are events only at the start and completion of a process, and nothing in between. What you need is an input that would allow you to specify intermediate points at which the conveyor notifies any objects that are watching the conveyor to update their states. This 'TriggerPointList' input would be generalised to apply to other objects such as Server.

In your example, the conveyor has a travel time of 10 seconds and you need an ExpressionThreshold to change state when an object is 2 seconds from the end. The 'TriggerPointList' input would be set to { 0.8 }, indicating the fraction of the total travel time for the watchers to be notified. For the ExpressionThreshold to be notified, its 'WatchList' input would include the conveyor. This arrangement would be very efficient, since the ExpressionThreshold would be evaluated only when notified by the objects it watches instead of evaluation at every event time for the entire model.

How does that sound to you?

Harry

[John Beasley]

Hi Harry. Thanks for getting back on this. I think the TriggerPointList seems a good generic way of achieving this. The suggested "new" version of EntityConveyor.java I sent over previously just put in a single point, so a list would be more flexible. As for effiency, yes, it really only adds a single event, so should not impair performance and remains true to the modelling/simulation philosophy. Let me know if you want me to test anything. 

Many thanks,

John

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[Lorenzo Ferro]

Dear Harry,

this new feature that you are going to introduce could be useful for me to model "real conveyors" (discontinuous and with behaviour depending on the inlet entity), linking the  'TriggerPointList' to ExpressionThresholds to command EntityConveyor Threshoulds, or linking the  'TriggerPointList'  to ExpressionEntities to change maybe the conveyor speed (or change the behaviour of other objects in the model).

I've some questions:

1) could the 'TriggerPointList' be the output of an Input Builder formula?

2) could the 'TriggerPointList' be triggered "in the actual sequence" even if the Conveyor speed is set to zero? (so that I can change the conveyor speed as soon as one specific intermediate point has been triggered, having the entity appear and run in a specific point of the conveyor?)

Thank you,

Lorenzo