Calculation of stop distance

kamenges said:

This is an extension of V=a²j but you know V and you specify time.

Click to expand...

Keith, your units don't work out.
I will let you work out the equation.

I personally don't like this method since the acceleration rate isn't bounded. The user needs to make sure in aseparate step that the maximum permissable acceleration rate isn't exceeded.

Click to expand...

Sometimes you have no choice because the speed is low and the distance to stop is small and the maximum deceleration rate is never reached. Both cases should be supported.

You are correct. That should have been:

V = a²/j

My typing, she ain't so good sometimes.

Originally posted by Peter Nachtwey:

Sometimes you have no choice because the speed is low and the distance to stop is small ...

Click to expand...

In this case we aren't talking about "that" case. Such a 5 or 6 posts back I proposed a method of defining a speed profile by simply indicating the time allowed to stop and assuming the whole stop profile would be in jerk. So as you go faster or decrease the available time the jerk rate increases. This is what I was referring to. But you are correct in your context. Both V < a²/j and V >= a²/j need to be handled.

Keith

All of this seems awfully complicated. For most of our machines in the cable manufacturing industry, we use Linespeed squared x Factor to set a ramp down bit. The factor = ramp length / Linespeed squared. This works for 99% of our applications.

This is non sense. It is either ignorance or making fun of what has been posted

mjoubert said:

All of this seems awfully complicated. For most of our machines in the cable manufacturing industry, we use Linespeed squared x Factor to set a ramp down bit. The factor = ramp length / Linespeed squared.

Click to expand...

What are you calculating? Do you realize that Linespeed squared cancels out leaving only ramp length?

This works for 99% of our applications.

Click to expand...

What laws of physics or math make these machines different?

Compare the actual length to [set length - ramp length] and latch a Ramp bit in the PLC. The ramp bit removes the direction input on the drive. Keep the drive enabled.

The ramp length is calculated by Linespeed (0-30m/s)² x f.

The method I describe above is for a stop to length application where the lengths are anywhere between 300 and 20 000 meters, depending on the process.

I haven't tried this with a motion control application as we normally use a cam or positioner drive and write the setpoints directly to the drive.

This is an old thread, is there any more interest; or another newer thread?