What is the acceleration on the AStar network?

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Axel Kohonen asked Sep 22 2016 at 8:02 AM Axel Kohonen commented Sep 26 2016 at 6:38 AM

What is the acceleration on the AStar network?

Hi,

I have a model in FlexSim 16.2 where I use the AStar navigator (astaracceleration.fsm). It seems that the acceleration and deceleration values given to a task executer are not used with AStar. There is nothing about this in the manual that I can find though.

Am I correct in my observations? And is there some way to get around this if I want an operator to have super high acceleration and deceleration. And how does AStar figure out the travel time? It seems to be using some acceleration/deceleration value/time behind the scenes.

Thank you!

Kind regards,

Axel

Software Version:

FlexSim 16.2.0

astar acceleration

astaracceleration.fsm (150.9 KiB)

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Answer 1 · 2016-09-22T17:45:45Z

Jordan Johnson answered Sep 22 2016 at 5:45 PM Axel Kohonen commented Sep 26 2016 at 6:38 AM

AStar builds kinematics, which is how it gives the travel path to a TaskExecutor. Those kinematics don't use acceleration (the addkinematic() command sets acceleration and deceleration to 0). @anthony.johnson may know more about this. For now, however, the acceleration and deceleration are not configurable on AStar.

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Axel Kohonen commented · Sep 23 2016 at 4:25 AM

Hi @jordan.johnson

Thank you for the explanation! That makes sense. Would be good to get a line or two about this in the user manual. As well as an explanation on what kind of acceleration/deceleration kind of ramp the kinematics use with AStar. As There is some time added as the travel time is longer than the distance/max speed.

In some cases it is much easier to use AStar than to define network paths or so, but to get exactly the travel times that one wants (and generally acceleration/deceleration values are not known, but only max speed) it would be great if one could set AStar to use instantaneous (or almost) acceleration. Or at least know exactly what AStar does behind the scenes.

Thank you!

Axel

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Phil BoBo ♦♦ Axel Kohonen commented · Sep 23 2016 at 3:35 PM

AStar has no acceleration/deceleration.

"As there is some time added as the travel time is longer than the distance/max speed." This is an incorrect statement.

The only times where acceleration/deceleration are used in the model you attached are in the offset tasks, which are not being done by the AStar Navigator.

In your operator's properties, select "Do not travel offsets for load/unload tasks." Then it will behave exactly as you want it to, with instantaneous acceleration and deceleration.

Attached is an example model that shows that this is the case.

The operator has a max speed of 1 meter/second, travels exactly 15 meters, and takes exactly 15 seconds.

If you change the operator's max speed to 3 meters/second, it will travel exactly 15 meters and take exactly 5 seconds.

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astar-has-no-accel-decel.fsm (16.6 KiB)

Axel Kohonen Phil BoBo ♦♦ commented · Sep 26 2016 at 6:38 AM

Hi Phil,

Thank you! That makes sense. I had obviously misunderstood where the extra time came from.

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