In the 3 examples above I used a natural frequency of only 50 Hz. You can see the parameters I used at the bottom of each of the position vs time plots.
The only things that are different between the 3 plots are the gains and how many feed forward gains are being used.
The first two plots use exactly the same feed forwards gains. My research has shown there isn’t much difference between PI and PID control. They are both sub optimal.
The PID with second derivative ( PID2) allows for higher closed loop gains so the closed loop poles can be placed more aggressively.
Adding the jerk feed forward helps a lot but the third order feed forwards changes the jerk in steps.
In short, normal motion controllers that only use PID and velocity and acceleration feed forward are not near as good as what a RMC75 or RMC150 can do.
I realized this a long time when we only had the RMC100 with only PID gains with velocity and acceleration feed forwards. The only thing I could say is that
the control will be better with a higher natural frequency. The high natural solution was often very expensive because it requires bigger diameter cylinders, bigger valves, bigger pumps, bigger accumulators.
The Time Move Absolute will generate one 5th order motion segment for the whole move.
A Move Absolute will generate a 5th order motion profile for the ramp up, a constant velocity, and then a 5th order motion profile for the ramp down.
Yes, you can interrupt these moves by entering force control mode.
I will generate a modified cosine move for comparison.
The main point I want to make for this thread is that the 18/nf or 35/nf rules are bogus. There is no justification for them and shame on those that propagated these bogus “rules of thumb”
These “rules of thumb” are too conservative and don’t take advantage of what modern motion controllers can do. In addition, if one where to use this rule of thumb they would over design the hydraulics making them much more expensive than they need to be. This would make motors a better choice only because the hydraulic designers are ignorant what they could do if they only knew.