A axis not tanking negative values.

[FXSM]

Hello, i've been looking at the forum for some time now, but this is my first post.

 In my work we have a 3+2 mill machine made for styrofoam. The machine works fine, but we have some issues with the post processor.

 We are currently using FANUC 5x Mill which was given to use, but its doenst work the way we want to. So we started our mission to make it work like it should.

 The first problem was that it made some wind ups when it should. We manage to fix that, but to verify it we made some half cylinders and mill them in various directions, to test if it was working like it should. A clarification is that our machine is a head/head type and both C and A axis have -105° to -105° angles.

 But the problem is that there is one direction of milling it that it makes wind ups in every past. We know for sure that in this direction and position of the machine and axis it shouldnt make any wind ups. We know why it makes them, we just cant find what it is in the POST, we tried changing everything that we look online but nothing worked.

 Ill try to describe what it does: The half cylinder is lay down on the machine bed, and the direction of the cylinder is in Y axis, so.. it makes half circles in X axis rotating the A axis which is the one with the tool. The problem comes when it reaches 0°, it comes from 90° all the way down to 0° and then it wind ups instead of going continuously down to -90°. Its like it wont take any negative values on A axis. The weird thing and makes us wonder a lot, is that in all other positions of the cylinder what we have tried it (all the other 5 ones) it works just fine.

 Ill really appreciate if anyone has any type of suggestion or something to look at.

 Thanks to all.

Some clarifications: We are currently using Mastercam 2018 and we check things with CIMCO.

 Im adding our PSD in case someone wants to check some value and i added a jpg file with the view from CIMCO where you can see the little wind ups that it makes and the position of the cylinder, and it shows clearly that it have the capacity to go further but it wont.

Regards from Argentina.

ADV Technology 2015 MAX (2).pst

[huskermcdoogle]

Post a zip to go of your whole file.  It will be easier for us to help that way. 

Few stabs in the dark:

It could possibly in your mics int settings.  It could also be toolpath related.  You could also look at a related setting, though I'm not sure because you haven't given us much, is you should try changing bias_null from 0 to 1 in the post (post line 517).  IIRC this will make the post respect the misc ints for every operation.

Good Luck,

Husker

[FXSM]

12 hours ago, huskermcdoogle said:

Post a zip to go of your whole file.  It will be easier for us to help that way. 

Few stabs in the dark:

It could possibly in your mics int settings.  It could also be toolpath related.  You could also look at a related setting, though I'm not sure because you haven't given us much, is you should try changing bias_null from 0 to 1 in the post (post line 517).  IIRC this will make the post respect the misc ints for every operation.

Good Luck,

Husker

Hello, thanks for your reply.

Im uploading all the post files in a .zip and im adding our mastercam file and the result gcode . We have tried changing bias_null but got nothing. The big problem is that our A axis which is the secondary axis set in POST, wont go to negative values, but we have every set saying that it can, and in other types of positions of the cylinder it clearly goes to negative values, so when we position it like the .jpg it makes that small wind up that it should. We also try changing the values for the limits in every way we could think of but got nothing again. And if we set sec_bias to axis always negative, it makes the same toolpath but with negative values. And if leave to all positives it gives the same result but in positive, and if we leave it as 0 which is suppose to make a continuous move in A axis ,thats where it makes the wind up and doenst make the continuous move.

If you have anything else we can try or need some other information or file i can upload it.

 

FXSM.rar

[huskermcdoogle]

It's passing through a singularity. There is no direct way that I know of to do what you want with the post you have.  That said you could reorient the part to make the peak not pass directly through a singularity and would thus run well, though the head would always stay positive, it just wouldn't have to flip the C in one line, it would do it gradually and in a smooth fashion.

[FXSM]

4 hours ago, huskermcdoogle said:

It's passing through a singularity. There is no direct way that I know of to do what you want with the post you have.  That said you could reorient the part to make the peak not pass directly through a singularity and would thus run well, though the head would always stay positive, it just wouldn't have to flip the C in one line, it would do it gradually and in a smooth fashion. 

Hi, thanks for you answer.

What kind of singularities are you talking about?

We know that we can re-orient the cylinder and obtain a fluid motion but as we are trying to make a post that works well and with all shape and forms we need it to do the things right and how its suppose to work in all directions. For example if we put the cylinder vertically and we mill it, in one direction it makes 2 wind up in every pass, and thats ok because we know that physically our machine cant go there and it needs that wind up. That been said, in the lay down cylinder of the jpg of our post we know that in that direction and position it can go to negative values in A axis and make that half cylinder in one pass without that wind up. We are planning to use the machine for milling thing in styrofoam like characters and figures. So it makes a peack at 0 almost every time for the complex shapes that it will make. So if in one direction it wind ups and we cant control it, that wind up will make us loose a lot of time in the future.

Hope you can understand why its important to us and why we need to fix it.

[huskermcdoogle]

I totally understand what you are trying to do.  As far as I know the generic 5x post is not capable of passing through C0. A0. (the singularity) without flipping the C.  You can try until you are blue in the face, without writing your own post from scratch or hiring someone to write a special post for you, you are not going to do what you want.  I have dealt with this problem time and time again and have never found an easy solution such a just configuring settings in the generic post, and using misc ints to control the behavior.  It may be possible that folks from CNC or the reseller network that have the source code for the binned portion of the post could easily configure the generic post to act as you require (thus making it a non "generic" post.

[huskermcdoogle]

On 11/15/2018 at 3:05 PM, FXSM said:

What kind of singularities are you talking about?

The singularity is caused when the tool vector goes vertical.  Due to the nature of trig functions, when the unit vector gets close to zero or one, the angle change is very rapid.  So any little error side to side in the vector will cause an axis to flip.  Therefore, the post is setup to prioritize one axis over the other.  In your case it is set to prioritize the primary axis (C) instead of the secondary axis (A).  It calculates the primary from the unit vector, then resolves the secondary angle.

The logic to handle axis behaviour through a singularity isn't terribly complicated, though would be somewhat different for every kinematic arrangement of machine, thus the reason it isn't well incorporated into the generic post.  Basically it entails some level of buffering and processing of future and previous feed moves to check what the rate of change of each axis is doing and make a logical decision as to which angle combination to output based on the logical rules you have set forth.  Actual application of said logic is not a trivial affair without an unbinned post and knowledge of the logic that it has in it already.  Some generic CAM posts, such as the one that moduleworks has developed have logic built into it to handle singularities, and you can configure it to handle things as you want on a case by case basis.  But MC doesn't use their post software, so don't get your hopes up.

[jlw™]

There are quite a few things you can do to prevent singularity.  The easiest way is to use lead/lag or tilt in the tool path.  The next method is to adjust your fixture so the part is oriented to prevent singularity.  Your goal is to make it so that there is only one possible solution for the machine to resolve or to pass thru the singularity in smooth motion.

I saw this article a couple months ago, pretty good:

https://www.researchgate.net/publication/322236560_Singularity_avoidance_for_five-axis_machine_tools_through_introducing_geometrical_constraints

[FXSM]

Hi, thank both of you. Now i understand a little bit more about the subject.

We have tried to set from MC the C axis with a little angel to try to avoid the singularity, it kinda works but now it tends to rock back and forth continuously between a little range of angels. The one weird thing is that the machine tries to continuously compensate that angel and it doesnt seem optimal. Its not the perfect solution but now that we know what is it we can work around it and see if we can find something else or a better solution.

We have to make more test to see whats the minimal angel that we can set the C axis for it to work the best. We will let you guys now if we make any more progress. And yeah, maybe the best solution is to make it a non generic post. But for now we will keep trying to fix it on our own haha.

Thank you all and if you find out something new let us now.

[jlw™]

Can you share a file?

[FXSM]

3 hours ago, jlw™ said:

Can you share a file?

Hi, yeah no problem.

I uploaded the gcode, post and mastercam file.

It makes a little dent where it made the wind up before. But like i said before, we are going to mill styrofoam, so if in that part it comes out a little rough its not a big deal for us, we prefer that before having like 32021 wind ups that we cant control.

 

 

FXSM 2.rar