Burning Bridges

The system offers 9 kinds of burning bridges:

1. Gap

2. Double-centered bridge (positive or negative)

3. Single-centered bridge

4. Cross-centered bridge

5. Double asymmetric bridge (positive or negative)

6. Single asymmetric bridge

7. Cross asymmetric bridge

8. Double asymmetric bridge in cutout

9. Gap including cut free geometry

Figure 3:1. Illustration of the Bridge Types 1-7

centered and asymmetric refer to how the bridge will be positioned relative to the cursor positions defining the bridge. A bridge can be defined with one or two cursor positions defining a "control line". A centered bridge is positioned so that the "control line" is in the center of the bridge, while an asymmetric bridge is positioned so that the "control line" coincides with a bridge line or (for cross bridges) one end of the cross (see picture).

Bridges of types 3, 5, 6 and 7 also need a position to determine the side, that means, the side where to place the gaps (types 3 and 6) or the side where to place the second bridge line (type 5) or side where to place the cross (type 7). The width of the bridges is part of the default information.

Type 1, gap, is the simplest of the bridges and can be defined using either one or two cursor positions. The system works in the following way, when a gap is defined.

• A given position is used to identify the closest part contour. The foot point on that contour will be calculated and the gap will be placed around that foot point.

• If the gap is defined by using two cursor positions, the first position is used to identify the closest part contour. If the activity code for node point preference is > 0 and the given point is within this distance from the node point, then the first gap line will pass through the node point. The second position is used to indicate on which side the second gap line shall be placed.

• If the distance from the node point is larger than the one given by the defaults the result is the same as with one cursor position.

A bridge defined with one cursor position will be treated by the system in the following way.

• The given position is used to identify the two closest part contours. On each contour, the foot point will be calculated and the line between the two foot points will be the control line.

A bridge defined with two cursor positions will be treated by the system in the following way.

• The line between the two given positions will be used to intersect the two closest part contours. The line between the two intersection points will be the control line.

Bridges can also be defined with a bridge line from a node point on one contour to a node point on another contour (for example, at common cutouts). Such a bridge must be created using one cursor position, and the default information controls the feature.

Bridges can also be defined to have a forced vertical direction (types 2, 3, 5 and 6) by setting a default value. If no intersection between the contours exists or if the bridge lines get too long, an ordinary bridge will be created.

The bridge of type 8 is defined in the same way as the bridge of type 5. The difference is that the bridge lines connect segments in the same contour in the bridge of type 8.

• This bridge is used in cutouts and when the tool path is verified (cf.VERIFY) the cutout will be burned as a hole.

When the gap of type 9 is used the operator has the possibility to define a cut free geometry which has its origin in the gap. The gap itself is identical to the type 1 gap.

• The cut free geometry is a string line with an arbitrary number of line segments. When the last point is closer to a plate part or the raw plate edge than a default distance, this point will automatically be adjusted so that the point will be situated this default distance from the plate part/raw plate edge.

• The cut free geometry will automatically be included in the verification of the tool path. The automatic restart facility is then used to resume the burning of the plate part.

The bridges of type 2 and type 5 can be defined either as positive or negative. It is possible to switch between positive and negative by pressing REJECT when the system prompts the user to give the first point defining the bridge. The default type is positive.

All bridges defined with two cursor positions can be made either horizontal or vertical. This is achieved by giving LOCK V or LOCK U before the second position is defined.