Control system for multi-axis simultaneous motion on high end CNC machines

[raptor1956]

I'm fascinated by the high end CNC machines that can coordinate 5-axis to machine parts at high speed with precision in the 10um range or even better.  There's a number of pieces that goes into it, of course, but the idea of being able to machine, applying force in several directions and directions that change dynamically, and to synchronize all 5-axis to do that simultaneously is, quite frankly, amazing.  One of the newer things is the use of linear drives for some of the axis which would appear to offer, in addition to a speed increase, virtually zero backlash.  Here's what I mean...



So, getting down to details it would seem that for some of these machines like the linear series they must use linear encoders and likely absolute ones at that and also with resolutions around 1um and perhaps better -- pretty amazing if you ask me.  But, perhaps the thing that amazes me most of all is the ability to coordinate all 5 axis at the same time, at high speed, and with precision below 10um. 

Some of these machines have spindles capable of more than 45,000rpm and others over 75hp -- insane!

These YT videos are like tool porn...


Brian

[IconicPCB]

check  out linuxCNC.

I am presently running two machines based on linuxCNC .

One a 3 axis milling machine with 100KRPM spindle @350W.  The other  with linear motors driving a solid state uv laser diode at half a G acceleration and 250mm/second speed.

[duak]

I've worked on a few CNC lathes & mills that were built between 1985 and 2005.  All the electronics got a lot smaller and more refined - very much like PCs and other consumer electronics.  The section of the CNC machine that interpolates the tool path and generates the axis postioning information is very much like a graphics engine in a workstation and uses some of the same algorithms.  The interpolator often looks ahead - some manufacturers quote a thousand points - to try to optimize the tool path to smooth it out.

My hat is really off to the people that developed the software that takes a 3D design file and generates toolpath data for a CNC machine to interpret.  The Multi-axis stuff is way beyond my pay grade.  This software isn't perfect - a machinist still has to debug and massage the data to get the best results.

Since these machines are powerful and work with tough materials, faults, failures & f-ups can be impressive.  I have a piece of steel that has a hole partly melted through it because the mill grabbed the wrong tool and tried to push it in at 8000 RPM.  Look up "stir welding".

The cutting tool technology is also amazing.  Tungsten carbide cutters work better at higher speeds.  In Steel, it you hit it hard enough, the shock wave actually liquifies the material ahead of the edge and the tool wipes it off rather than slicing it off.  The energy needed is reduced and the tool life is increased.

[raptor1956]

I've worked on a few CNC lathes & mills that were built between 1985 and 2005.  All the electronics got a lot smaller and more refined - very much like PCs and other consumer electronics.  The section of the CNC machine that interpolates the tool path and generates the axis postioning information is very much like a graphics engine in a workstation and uses some of the same algorithms.  The interpolator often looks ahead - some manufacturers quote a thousand points - to try to optimize the tool path to smooth it out.

My hat is really off to the people that developed the software that takes a 3D design file and generates toolpath data for a CNC machine to interpret.  The Multi-axis stuff is way beyond my pay grade.  This software isn't perfect - a machinist still has to debug and massage the data to get the best results.

Since these machines are powerful and work with tough materials, faults, failures & f-ups can be impressive.  I have a piece of steel that has a hole partly melted through it because the mill grabbed the wrong tool and tried to push it in at 8000 RPM.  Look up "stir welding".

The cutting tool technology is also amazing.  Tungsten carbide cutters work better at higher speeds.  In Steel, it you hit it hard enough, the shock wave actually liquifies the material ahead of the edge and the tool wipes it off rather than slicing it off.  The energy needed is reduced and the tool life is increased.

Yeah, there's a lot more to be impressed with than the control system which is impressive to be sure.  The idea of cutting quickly through stainless steel blows my mind given the struggles I've had over the years with that stuff.

The tool path interpolation that has to take into account things like backlash and do so for all 5 axis at the same time is pretty staggering.  I'm not at all surprised the something like a GPU would be used but what I find hard to comprehend is how they were doing this back in the late 80's -- 30 years ago.  Surely the current generation of CNC machines are much beyond what was possible back then, but the fact they were doing simultaneous 5 axis work back then is hard to fathom. 

One interesting thought is about the progression of technology and the ability to make parts with a given tolerance.  If the state of the art at some point is, say, 10um then how do you build a machine capable of, say, 5um.

Another interesting thought is how long would it take to get to where we are today if by some stroke all our machines and equipment were to disappear.  If we were thrown back to the stone age in terms of tools and machines yet we still had the knowledge how long would it take to get back to where we are -- I'd guess a minimum of 25 years but it cold well be more than 100.  From the beginning of the industrial revolution until now is, about, 250 years so it wouldn't take that long to return, but you don't go from hitting things with hammers to machining a 3D object from titanium overnight.


Brian

[Rerouter]

Most machinist are very familiar with building higher precision tools than the ones they have on hand. e.g. a blacksmith making there first hammer.

So the mechanics of those machine shops would be back to a similar standard in months, just manually operated, so slower than before, the electronics will take a while longer, but its not too many steps to get back to 1980's level IC lithography, and from there, with already existing knowledge, its not many leaps and bounds to get back to where we where.

If your laying out a PCB, and you loose power, it doesn't take you anywhere near the time it originally took to get back to where you where, as you remember most of the general choices you made that resulted in that pattern. same goes for silicon, if you have spent years laying it out, you remember the structures and can quickly build up something that does the job.