Mach 4 5-ax post processor - A&C axes move too slow

[Anonymous]

Hey all -

Have a bit of a mutant 5-ax Mach4 machine that is pretty heavily customized. Most of the bits appear to be working well, but the part I cannot seem to figure out is that the A&C axes appear to be moving at the incorrect speed on the tool itself.

I have the fusion file attached as well as my post processor.

Things I have checked on the tool itself:

Motor tuning on Mach4 itself - we can move 90deg in about 0.2sec on both the A & C axes, and measured motion equals the programmed jog distance (i.e. the head physically moves 90deg when I program 90deg).

Why I suspect that something is wrong with the A&C inverse time feedrate calculation in the post is the slowdown appears very severe in sample files we are running with high A&C axis movement. This is not seen in files with minimal A&C movement.

In addition to the Mach4 post processor, I have also tried using a FANUC A-ax table post processor (that was then modified to move the A-ax into the head, and an additional axis created for C). That one produced similar feedrates as the Mach4 5-ax...so now I am thinking I am messing something up in my axis setup.

Any help would be greatly appreciated.

[daniel_lyall]

What is the max acc and velocity for the A and C?

[Anonymous]

Counts per unit on are 115

Velocity is 100000 units/min

Acc is 2000 units/sec^2

Same setting for both motors. These are kind of unworkably fast for the application, but specifically setup this way to eliminate the issue you are thinking about. 

The controller is following the programmed feed rates according to the on screen display in Mach4...tool simply slows down massively as the A axis changes from positive to negative direction. Fusion appears to be calculating the feedrates incorrectly.

[Anonymous · Accepted solution]

Of course, Murphy's law has won on this one. After beating my head on this for about a week, I finally got it sorted when I posted to the forum. The problem was quite simple really...

My intial axis definition for the 4th and 5th axes were incorrect. In the post which output the incorrect feedrates, this is what I was defining:

var aAxis = createAxis({coordinate:0, table:false, axis:[-1, 0, 0], offset:[-90,0,0], range:[-90,90], cyclic:false, preference:0});

var cAxis = createAxis({coordinate:2, table:false, axis:[0, 1, 0], offset:[0,0,-90], range:[-90,90], cyclic:false, preference:0});

machineConfiguration = new MachineConfiguration(aAxis, cAxis);

Everything was fine in the A-ax definition, but if you note in the C-ax, although I have coordinate:2 specified, I am defining the axis around the y axis, not the z axis. Thus, gcode was output as C position, but it was not properly used in the feedrate calculation. 

This simple changed fixed everything:

var aAxis = createAxis({coordinate:0, table:false, axis:[-1, 0, 0], range:[-90,90], cyclic:false, preference:0});

var cAxis = createAxis({coordinate:2, table:false, axis:[0, 0, 1], range:[-90,90], cyclic:false, preference:0});

machineConfiguration = new MachineConfiguration(aAxis, cAxis);

Always remember to take rest breaks when banging your head on the wall for too long :-D.

[daniel_lyall]

Or sit back and have a beer I find just talking to some who knows nothing about what you are doing works.

[RMILLERAUTO]

I’m having a slow problem as well but more like the speed and acceleration issue I believe.   Everything cuts and moves exactly as it should.  But if I program a feed rate of 40. I get a machine speed of 20  I can override the feed rate to say 150 and get things up to 30.  Can anyone help me remember why this happens.  If speed and velocity are too low On an axis everything is based off of the slowest axis or something right ?   Thanks