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Paul Toone posted Edwin Purwanto commented

Power and Free Systems   

Power and Free conveyor systems are designed for industrial applications that require more flexibility and a greater capacity than conventional conveyors. They provide the unique ability to stop individual loads without stopping the entire production line.

You can simulate both inverted and overhead power and free conveyors using FlexSim. In these systems, dogs travel at fixed intervals along a looping chain. These dogs pick up carriers in the system as they pass them. In simulation terms it is similar to having a moving space greater than stopping space (there is a caterpillar-like accumulation effect), except that the point at which an item can move on the conveyor is defined by the location of the next passing dog, instead of by the space between it and the item ahead of it.

The following image shows an example of a simple inverted Power and Free system in FlexSim:

In order to set up a Power and Free system in FlexSim, you need Straight or Curved Conveyors that have Conveyor Type Settings with Power and Free enabled. In this example, there are three conveyors (two Straight Conveyors and one connecting Curved Conveyor) and a Motor which is connected to all three conveyors. Although we use a Motor in this example, it is not technically required. Motors are only needed if the default dog positioning method is insufficient. Notice that there are also lines running across the conveyors to represent the dogs on the tracks.

To create this kind of Power and Free conveyor system:

  1. Add the conveyors and add any additional Fixed Resources such as Sources and Sinks. (See Adding Conveyors to a Simulation Model.)
  2. Connect the conveyors together and connect the conveyors to the Fixed Resources. (See Connecting Conveyors.)
  3. Place a Motor somewhere in the model.
  4. Connect the Motor to the conveyors. (See Adding Conveyors to a Motor.)
  5. Double-click the Motor to open its Properties dialog box. In the Motor tab, check the Sync Power and Free Dog Positions check box. If needed, you could also check the Adjust Dog Gap for Continuous Loop check box. (See Motors - Power and Free Settings.)

  1. If you would like, you could change the name of this new Conveyor Type by editing the top field. In this example, we'll change the name to PowerAndFree.
  2. Click OK to apply these settings and close the Properties dialog box. The PowerAndFree conveyor type should now appear in the list of Conveyor Types in the Conveyor System Tool.
  3. Double-click each merging conveyor to open its Properties dialog box. From the Conveyor Type menu, select the PowerAndFree conveyor type.

  1. Click OK to apply the settings and close the Properties dialog box. The conveyor will now inherit the Power and Free settings.
  2. To test the simulation, click Reset and Run on the simulation control bar. As the simulation runs, you will notice lines going across the conveyor to represent the dogs in the conveyor.
Overhead Power and Free Systems
To create an overhead power and free system, put a Decision Point or Photo Eye at the beginning (tail) of the first conveyor. On its OnArrival Trigger, select Movement then, click Translate Item. Set the Conveyor Up setting to a negative number, such as -2 or -zsize(item), and it will hang below the conveyor while moving. NOTE: You might also want to raise each conveyor's Z-axis so that they are higher off the ground.
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Edwin Purwanto avatar image Edwin Purwanto commented ·


Is there any way to check the content of a power and free conveyor? Like when it is 80% full or 100% full, we should divert the flowitem somewhere.

Best regards,


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paul.t contributed to this article


FlexSim 2016.1