Smoothness of arcs

22 May 2020 23:12 #168611 by Stephanisk
Hello everyone,

I have been working 2 years now with linuxcnc 2.8.0 master. Very happy with it. This week I have finally had time to be looking into enhancing configuration. This master branch has not been updated, I don't know how and don't dare to mess up my machine (I need it for living)

So I always got upset with the movements of my machine on small turns like helix movements. The machine always got some jerk or small slow every half circle. I really want to get rid of it.
I have always used g64 p0.1 q0.1 and I have slowed my acceleration seriously down so that when I move the machine per 1 mm I don't have any jerk because of machine weight. But I still have these little stops and jerks. I have reading 100 lines in advance (default was 50) and the arc cycle set to 8 (default was 4)

All motors are 1000w servos. System is in mm. Machine is a CNC gantry router for woodwork total weight 3500kg. Gantry is about 1000kg.

If I set the g64 to p0.5 and q0.5 my machine doesn't slow in any turns but that is 0.5mm out of accuracy that is way to much.

I read some people here can have perfect movement with as little as p0.01 and q0.01 I would love to know how they are doing this.

Another issue is that when milling aluminium the small stops disrupt the speeds and feeds needed to ensure smooth cutting without mills getting jammed up with sticking aluminium.

Would someone have an idea how I could get smoother motion without compromising on accuracy. Also is it worth it to update my 2.8.0 installation for traject planning?

Thanks for any help.

Please Log in or Create an account to join the conversation.

23 May 2020 02:48 #168637 by rodw
Replied by rodw on topic Smoothness of arcs
I wonder if this is caused by the Linuxcnc trapezoidal (straight line) acceleration model?
V's jerk limited or S bend acceleration profiles which do not exist in Linuxcnc.

So unless limited by segment length, we accelerate at the maximum velocity for an axis until we get to the commanded speeds, so the heavy weight induced inertia could result in a jerk at that point. Sadly apart from rewriting the trajectory planner, there is nothing that can be done about it.

Please Log in or Create an account to join the conversation.

26 May 2020 20:11 #169003 by Todd Zuercher
Replied by Todd Zuercher on topic Smoothness of arcs
There have been bugs reported in the past regarding the current motion planner in Linuxcnc. Especially regarding helical movements like you describe. I do not know if they have been addressed. I haven't followed the subject for quite some time.

Please Log in or Create an account to join the conversation.

Time to create page: 0.079 seconds
Powered by Kunena Forum