Why does power and free reset the current speed to default speed?

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Alessio Merlo asked May 10, '22 Alessio Merlo commented May 13, '22

Why does power and free reset the current speed to default speed?

Hi all,

I need to understand why the power and free option resets the current speed to the default speed when the conveyor receives the item for the first time with power and free option enabled.

I created a simple model to explain the issue:

1. simple source-conveyor-sink model;

2. conveyor default speed equal 1m/s;

3. after 10 s an user event set the conveyor current speed to 2m/s;

4. when the conveyor receives the first item, the current speed is 1m/s instead of 2m/s;

Is it a bug or a conveyor feature?

power_and_free_speed.fsm

Software Version:

FlexSim 22.1.1

conveyor power and free

power-and-free-speed.fsm (41.0 KiB)

Answer 1 · 2022-05-12T17:30:36Z

anthony.johnson answered May 12, '22 Alessio Merlo commented May 13, '22

This is a bug. We'll fix it for the next release. Felix's observations are correct. When in fixed-interval-movement mode, it doesn't initialize dog positions until it sees its first item, so that multiple chained conveyors can sync their dog positions somewhat automatically as the first item flows down them. Unfortunately this initialization code initializes the 'speed driver' based on the base speed of the conveyor. I did not consider that the user may have changed the target speed before the first initialization.

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Alessio Merlo commented · May 13, 2022 at 06:54 AM

Thanks @anthony!

I also sent an email to [email protected] with an issue into catch condition trigger of power and free. The current and item variables aren't defined well. If you have time, please fix it in the next release!

Thanks for your support!

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1652424314420.png (32.4 KiB)

Answer 2 · 2022-05-10T11:10:08Z

Felix Möhlmann answered May 10, '22 Alessio Merlo commented May 10, '22

This is mostly a guess:

As far as I understand it, the power and free system only gets 'initialized' once the first item enters the conveyor. (Before that, no dogs are visible on the conveyor.)

By connecting the conveyor to a motor and checking the 'Sync Power and Free Dog Positions' option, FlexSim will initialize the system on model start (dogs start to run immediately) and the speed change will not revert when an item enters the conveyor.

I believe this was done, so that even without syncing multiple conveyors by using a motor, the dog positions will still run uniformly across multiple sections. (Creating the first dog when the first item enters makes sure that the position of the dog would coincide with that of previous conveyor).

power-and-free-speed_1.fsm

1652181002201.png (145.9 KiB)

power-and-free-speed-1.fsm (41.2 KiB)

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Alessio Merlo commented · May 10, 2022 at 03:43 PM

Hi @ felix,

thank for your answer.

The motor is a valid workaround to solve my issue, but I don't understand the reason to change the conveyor speed when the first dog is created. @ phil, could you help us?

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