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realvirtual.io realvirtual v6.7.3

Bag Forming

Beta

Bag forming shows how a flow wrapper or a bag maker turns a running foil into single bags. Two components on the mesh of the foil strand do the work:

  • Mesh Stretch makes the strand grow out of the knife while the foil runs.
  • Mesh Cut cuts the strand at the knife angle. The cut piece becomes a part (an MU) at exactly the place where it was cut, with exactly the print it showed, and it leaves on the conveyor below it. The strand starts again at the knife.

Both components are part of the commercial edition (Beta).

Stretch, cut, hand over The strand grows from the knife by the foil travel. At the knife angle the grown piece is copied into a part at the same place with the same print, the strand starts again at the knife, and the conveyor below takes the part over. 1 · Stretch uv.y = 0 stays uv.y = 1 moves by Extrusion knife 2 · Cut knife at 180° or SignalCut same place, same print 3 · Hand over strand starts again the belt below takes the part
The strand grows from the knife, the grown piece is cut into a part at the same place, and the conveyor below carries it away.

Setting it up

Section titled “Setting it up”
  1. Give the strand its own mesh node. Its V texture coordinate decides which vertices move: with Weight Source UV, vertices with V ≤ 0 stay and vertices with V ≥ 1 move by the whole extrusion; InverseUV swaps the two ends. The moving end rests at the knife.
  2. Add Mesh Stretch to the strand. Choose the Axis and Direction the strand grows in, and connect Signal Extrusion to the foil travel since the last cut (mm), or set Source Drive to the foil drive.
  3. Add Mesh Cut to the same node. Set Cut Drive to the knife drive and enter the knife angle in Cut Positions, or connect Signal Cut.
  4. Put a Transport Surface under the place where the strand is cut, and a Sink at its end.

Mesh Stretch

Section titled “Mesh Stretch”
PropertyWhat it does
AxisLocal axis the strand grows along (X, Y or Z, as in Unity).
DirectionNegative or Positive along the axis.
Weight SourceWhich end of the strand moves: UV = the vertices with V ≥ 1 (as the Unity Extrudeable shader), InverseUV = the vertices with V ≤ 0, for a strand whose UVs run the other way.
ExtrusionCurrent stretch in mm, shown live.
Max Extrusion MmUpper limit of the stretch in mm; 0 = no limit.
Scroll TextureThe print moves with the stretch.
Texture Mm Per UnitLength in mm of one texture repeat along the strand; 0 = taken from the mesh. A negative value reverses the print direction.
Signal ExtrusionPLC output with the stretch in mm. The controller owns the value: a cut does not reset it, the controller sets it back to 0 itself.
Source DriveThe foil drive. The component adds up the forward travel of the drive itself, and a cut takes the cut length off.

Use either Signal Extrusion or Source Drive. When both are set, the inspector shows a warning and the signal is used.

The extrusion is a real length: a scaled parent node does not change how far the strand grows.

Mesh Cut

Section titled “Mesh Cut”
PropertyWhat it does
Cut PositionsDrive angles in degrees. Each position cuts once per revolution while the knife turns forward; turning back never cuts, and passing the same angle again after turning back does not cut twice.
Cut DriveThe knife drive whose angle is compared with Cut Positions.
Signal CutPLC output; a rising edge cuts. A knife crossing and the signal in the same cycle make one cut.
Signal Cut CountPLC input that receives the number of cuts since the last reset.
Place On Transport SurfaceThe cut part is handed to the transport: the conveyor it overlaps takes it over. Off: the part stays where it was cut.
Take ChildrenParts lying completely inside the cut piece become its load and travel with it, for example the product in the bag.
Cut ModeGrown: the part is only the material that grew beyond the knife, cut exactly at the knife plane with the same print. Whole: the part is a copy of the whole strand mesh.
Min Cut Length MmA cut with less stretch than this makes no part: the short end is scrap, as the first bag after a start. 0 = every cut makes a part.

At most one cut is made per simulation step; a second crossing in the same step is made up in the next step. After a reset the first step only arms the cut, so a reset or a reconnect never produces an extra bag.

Foil print on the web

Section titled “Foil print on the web”

The foil before the knife usually runs as a Transport Surface that scrolls its print. For a foil roll, set Static Face Axis to the roll axis so the end faces of the roll keep a still print, and use Texture Tiling to match the print length.

See also

Section titled “See also”