Feedrate planning at zero speed

Hi Raoul,
In the HPC paper, the remaining time is approximated by the following equation:

image

I’m wondering if this strategy could also be used for singularity handling. At the start of zero velocity, we can assume the q(u) to be linear, so we have the relation:

Then we have:

As q(uk) is a cubic spline and because q(0) is zero at start, we have q(u) to be the following format:

Substitute it into the denominator, we have:

This uk has a closed form of solution to be:

And we can choose the minimum positive solution.

We can use very small tk like 1e-8 to solve the uk, and the spline q(u) will be almost linear at the infinite-small range . Once we have the first solution, then we are safe to use Taylor series expansion to get the remaining uk.

Do you think the derivation is correct or did I mistake something?

Thanks!

dear Yakunix,

please find the attached pdf document prepared by my mathematician friend Philippe Blanc.
ZeroSpeedProblem.pdf (85.5 KB)

I hope this makes things clearer.

best regards

Thank you Raoul.

This explanation is cool!

In essence, the initial stage could not be approximated by the spline.

Hi Yakunix,
100% correct