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  • hmnijp
  • hmnijp
22 Jan 2025 15:11 - 23 Jan 2025 09:47
Replied by hmnijp on topic scurve trajectory planner

scurve trajectory planner

Category: General LinuxCNC Questions

 I always set with a P value the maximum allowed deviation of a given path. So now I am not really sure. Can I just calculate something?     
 

Yes. Such smoothing is not optimal. The value of P should certainly be the limit of deviation from the programmed path.

I am also concerned about the compression algorithm that creates polygons if you increase the ‘P’ value. I have prepared a comparison with the old path planner:
 
 

It shows that first the polyline is compressed by an algorithm similar to Douglas-Peucker, then the large lines are connected by a b-spline whose radius of curvature is limited by acceleration.  This creates constant changes in velocity, acceleration and deceleration that are bad for milling. The most important thing for milling is to maintain a stable speed. The optimum solution would be to drive with minimum curvature over the entire trajectory. The last image shows the difference in 3D milling.
 
 

The old planner produces a path with minimal curvature, but it always tends to move inside the curve. A similar effect can be seen in this animation comparing "Moving Average" and "CCMA": 
github.com/UniBwTAS/ccma/raw/master/figures/demo.gif


I also have a problem when the trajectory is plotted with a lot of smoothing errors - it randomly moves far outside the limits:


I can provide all the programs I used for the comparison, maybe it will help to fix the errors. 
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