Re: [Emc-users] Split X axis - How to go about that?

[andy pugh]

On 17 November 2015 at 17:18, Marius Liebenberg  wrote:

> has anyone attempted this kind of silly
> arrangement?

https://forum.linuxcnc.org/forum/46-francais/28479-cinematique-avec-axes-redondants-presentation?limitstart=0#52533


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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

That will work if you always have tubes that are longer than 3000mm. If 
you need to cut shorter that half the distance then only one motor will 
move and then the scale will be broken. This is way I thought that some 
hand-off might be the answer.
Or am I not seeing the whole picture with the two steppers moving 
together but always in opposite directions?

Would this mean that the zero position will have both motors sitting in 
the middle?

-- Original Message --
From: "John Kasunich" <jmkasun...@fastmail.fm>
To: emc-users@lists.sourceforge.net
Sent: 2015-11-17 20:04:56
Subject: Re: [Emc-users] Split X axis - How to go about that?

>Instead of a hand-off you could run both axes all the time.  If you 
>command a 100mm move,
>the main axis would move 50mm and the auxiliary axis would also move 
>50mm.
>
>To do that with steppers you could simply send the same step pulses to 
>both motors (if they
>have the same steps-per-mm).  Then tell LinuxCNC that the steps-per-mm 
>is half of the
>value for each motor.
>
>Homing might be a challenge.  You would like the home switch for each 
>axis to cut off
>the step pulses for that axis, and not tell LinuxCNC that the switch 
>has been hit until
>the machine actually hits both switches.  HAL can do that if you are 
>doing software
>stepping.
>
>
>
>On Tue, Nov 17, 2015, at 12:51 PM, Marius Liebenberg wrote:
>>  That will work for servos but in my case I am using steppers. Not 
>>sure
>>  if the problem is the same. I want the axis to be spit in two and the
>>  controller must know when to use what stepper to get all the way from 
>>0
>>  to 6000mm. Somewhere in the middle there must be some sort of 
>>handover
>>  between the two steppers.
>>
>>
>>:
>>  >
>>  >>  has anyone attempted this kind of silly
>>  >>  arrangement?
>>  >
>>  
>> >https://forum.linuxcnc.org/forum/46-francais/28479-cinematique-avec-axes-redondants-presentation?limitstart=0#52533
>>  >
>>  >
>>  >--
>>  >atp
>>  >If you can't fix it, you don't own it.
>>  >http://www.ifixit.com/Manifesto
>>  
>>--
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>
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Re: [Emc-users] Split X axis - How to go about that?

[John Kasunich]

Instead of a hand-off you could run both axes all the time.  If you command a 
100mm move,
the main axis would move 50mm and the auxiliary axis would also move 50mm.

To do that with steppers you could simply send the same step pulses to both 
motors (if they
have the same steps-per-mm).  Then tell LinuxCNC that the steps-per-mm is half 
of the 
value for each motor.

Homing might be a challenge.  You would like the home switch for each axis to 
cut off 
the step pulses for that axis, and not tell LinuxCNC that the switch has been 
hit until
the machine actually hits both switches.  HAL can do that if you are doing 
software 
stepping.



On Tue, Nov 17, 2015, at 12:51 PM, Marius Liebenberg wrote:
> That will work for servos but in my case I am using steppers. Not sure 
> if the problem is the same. I want the axis to be spit in two and the 
> controller must know when to use what stepper to get all the way from 0 
> to 6000mm. Somewhere in the middle there must be some sort of handover 
> between the two steppers.
> 
> 
>   :
> >
> >>  has anyone attempted this kind of silly
> >>  arrangement?
> >
> >https://forum.linuxcnc.org/forum/46-francais/28479-cinematique-avec-axes-redondants-presentation?limitstart=0#52533
> >
> >
> >--
> >atp
> >If you can't fix it, you don't own it.
> >http://www.ifixit.com/Manifesto
> --
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users


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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

That will work for servos but in my case I am using steppers. Not sure 
if the problem is the same. I want the axis to be spit in two and the 
controller must know when to use what stepper to get all the way from 0 
to 6000mm. Somewhere in the middle there must be some sort of handover 
between the two steppers.


  :
>
>>  has anyone attempted this kind of silly
>>  arrangement?
>
>https://forum.linuxcnc.org/forum/46-francais/28479-cinematique-avec-axes-redondants-presentation?limitstart=0#52533
>
>
>--
>atp
>If you can't fix it, you don't own it.
>http://www.ifixit.com/Manifesto
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Re: [Emc-users] Split X axis - How to go about that?

[John Kasunich]

My mental picture of your machine might not be accurate.

I'm visualizing a cutting head that moves along an axis using one motor,
and another motor that moves the entire axis.  If that is wrong then the
rest is wrong too.

Anyway, assume that home = 0, and when homed the cutter head
is at the far left end of the "movable axis", and the moveable axis is
also at the far left end of the machine frame.  If you then command 
500mm, the movable axis moves 250mm to the right, and the head
moves 250mm to the right relative to the moveable axis.  That means
the net movement of the head is 500mm.

If my mental picture is wrong, can you correct it?  Maybe with a real
picture or a sketch or something?

John Kasunich

On Tue, Nov 17, 2015, at 01:17 PM, Marius Liebenberg wrote:
> That will work if you always have tubes that are longer than 3000mm. If 
> you need to cut shorter that half the distance then only one motor will 
> move and then the scale will be broken. This is way I thought that some 
> hand-off might be the answer.
> Or am I not seeing the whole picture with the two steppers moving 
> together but always in opposite directions?
> 
> Would this mean that the zero position will have both motors sitting in 
> the middle?
> 
> -- Original Message --
> From: "John Kasunich" <jmkasun...@fastmail.fm>
> To: emc-users@lists.sourceforge.net
> Sent: 2015-11-17 20:04:56
> Subject: Re: [Emc-users] Split X axis - How to go about that?
> 
> >Instead of a hand-off you could run both axes all the time.  If you 
> >command a 100mm move,
> >the main axis would move 50mm and the auxiliary axis would also move 
> >50mm.
> >
> >To do that with steppers you could simply send the same step pulses to 
> >both motors (if they
> >have the same steps-per-mm).  Then tell LinuxCNC that the steps-per-mm 
> >is half of the
> >value for each motor.
> >
> >Homing might be a challenge.  You would like the home switch for each 
> >axis to cut off
> >the step pulses for that axis, and not tell LinuxCNC that the switch 
> >has been hit until
> >the machine actually hits both switches.  HAL can do that if you are 
> >doing software
> >stepping.
> >
> >
> >
> >On Tue, Nov 17, 2015, at 12:51 PM, Marius Liebenberg wrote:
> >>  That will work for servos but in my case I am using steppers. Not 
> >>sure
> >>  if the problem is the same. I want the axis to be spit in two and the
> >>  controller must know when to use what stepper to get all the way from 
> >>0
> >>  to 6000mm. Somewhere in the middle there must be some sort of 
> >>handover
> >>  between the two steppers.
> >>
> >>
> >>:
> >>  >
> >>  >>  has anyone attempted this kind of silly
> >>  >>  arrangement?
> >>  >
> >>  
> >> >https://forum.linuxcnc.org/forum/46-francais/28479-cinematique-avec-axes-redondants-presentation?limitstart=0#52533
> >>  >
> >>  >
> >>  >--
> >>  >atp
> >>  >If you can't fix it, you don't own it.
> >>  >http://www.ifixit.com/Manifesto
> >>  
> >>--
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> >
> >
> >--
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> >   jmkasun...@fastmail.fm
> >
> >--
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Re: [Emc-users] Split X axis - How to go about that?

[Viesturs Lācis]

2015-11-17 21:54 GMT+02:00 John Kasunich :
> Just divide the steps per mm for X in half, and send the X steps to both
> gantry and pipe chuck motors using HAL.  Also send X direction to both
> motors, and invert one so they travel in opposite directions.  Use HAL
> logic (in the base thread) to turn off steps to each motor when that motor
> hits its home switch (only while homing), and to send a composite home
> switch signal to LinuxCNC when both motors have hit their home switches.

Why not to treat the chuck motor as another joint of X axis? There
already are 2 of them (on the gantry), so adding 3rd should be
straightforward - that allows homing the chuck to its own switch
without any additional hassle in HAL or whatever.

Viesturs

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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

-- Original Message --
From: "andy pugh" <bodge...@gmail.com>
To: "Enhanced Machine Controller (EMC)" 
<emc-users@lists.sourceforge.net>

Sent: 2015-11-17 22:06:15
Subject: Re: [Emc-users] Split X axis - How to go about that?

On 17 November 2015 at 20:00, Viesturs Lācis <viesturs.la...@gmail.com> 
wrote:



 Why not to treat the chuck motor as another joint of X axis? There
 already are 2 of them (on the gantry), so adding 3rd should be
 straightforward


That ought to work, for the first ever XYZAXX config


Living on the edge always :)


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Re: [Emc-users] Split X axis - How to go about that?

[Viesturs Lācis]

2015-11-17 22:23 GMT+02:00 Marius Liebenberg :
>>Why not to treat the chuck motor as another joint of X axis? There
>>already are 2 of them (on the gantry), so adding 3rd should be
>>straightforward - that allows homing the chuck to its own switch
>>without any additional hassle in HAL or whatever.
>>
> I probably dont have an idea of how that works. I am not good with
> joints mode.

You already have 2 joints assigned to X axis on the gantry. Or am I
missing something? So I think that adding 3d joint to the same X axis
in HAL should be trivial.

Viesturs

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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

>A picture truly is worth 1000 words
>
>So, to cut a zero length pipe, you put the pipe chuck all the way to 
>the left and the torch carriage all the way to the right.
>
>To cut a 500mm pipe, you move the pipe chuck 250 mm to the right and 
>the torch carriage 250mm to the left from the "zero length pipe" 
>position.
>
>To cut a 6000mm pipe, you move the pipe chuck 3000mm to the right and 
>the torch carriage 3000mm to the right from the "zero length pipe" 
>position.
>
>The two carriages always move the exact same distance but in opposite 
>directions.
>
>Does that work?
>
That seems to be as I understand it then. Two configs is no problem as 
the machine will only do one at a time

>One problem would be that when running pipe work you need a different 
>machine configuration, such that when the g-code says to move 600mm, 
>LinuxCNC sends 300mm worth of steps to both axes.  When doing table 
>work and the g-code says to move 600mm, LinuxCNC sends 600mm worth of 
>steps to the table axis only.  The straightforward way is to re-start 
>LinuxCNC with a different configuration.  You might be able to do some 
>clever HAL stuff to make the switch without restarting.
>
>One question:  why not make the pipe chuck be a U axis, the torch 
>carriage is X, and let the g-code programmer have complete control of 
>what happens?  Move pipe only, torch only, or both, under g-code 
>control.


Not sure I understand how to use the U axis. I will be using the 
sheetcam rotary plugin to do the gcode. I will have to look at the usage 
of a U axis before I can decide on that.
>
>
>--
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>   jmkasun...@fastmail.fm
>
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Re: [Emc-users] Split X axis - How to go about that?

[John Kasunich]

On Tue, Nov 17, 2015, at 02:40 PM, Marius Liebenberg wrote:


> >One question:  why not make the pipe chuck be a U axis, the torch 
> >carriage is X, and let the g-code programmer have complete control of 
> >what happens?  Move pipe only, torch only, or both, under g-code 
> >control.
> 
> 
> Not sure I understand how to use the U axis. I will be using the 
> sheetcam rotary plugin to do the gcode. I will have to look at the usage 
> of a U axis before I can decide on that.

If you are using CAM it probably makes sense to skip the U axis.
If you were writing your own G-code the U axis would give you more
flexibility, but the CAM won't understand it anyway.

Just divide the steps per mm for X in half, and send the X steps to both 
gantry and pipe chuck motors using HAL.  Also send X direction to both
motors, and invert one so they travel in opposite directions.  Use HAL 
logic (in the base thread) to turn off steps to each motor when that motor
hits its home switch (only while homing), and to send a composite home
switch signal to LinuxCNC when both motors have hit their home switches.

If you are generating step pulses in hardware (Mesa, Pico, or other) then
things get a little more interesting.  More like a servo system, still doable
but the approach is a little different.


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Re: [Emc-users] Split X axis - How to go about that?

[John Kasunich]

On Tue, Nov 17, 2015, at 02:10 PM, Marius Liebenberg wrote:
> 
> Ok the picture is attached. It is a bit different from what you saw :)
> 

A picture truly is worth 1000 words  

So, to cut a zero length pipe, you put the pipe chuck all the way to the left 
and the torch carriage all the way to the right.

To cut a 500mm pipe, you move the pipe chuck 250 mm to the right and the torch 
carriage 250mm to the left from the "zero length pipe" position.

To cut a 6000mm pipe, you move the pipe chuck 3000mm to the right and the torch 
carriage 3000mm to the right from the "zero length pipe" position.

The two carriages always move the exact same distance but in opposite 
directions.

Does that work?

One problem would be that when running pipe work you need a different machine 
configuration, such that when the g-code says to move 600mm, LinuxCNC sends 
300mm worth of steps to both axes.  When doing table work and the g-code says 
to move 600mm, LinuxCNC sends 600mm worth of steps to the table axis only.  The 
straightforward way is to re-start LinuxCNC with a different configuration.  
You might be able to do some clever HAL stuff to make the switch without 
restarting.

One question:  why not make the pipe chuck be a U axis, the torch carriage is 
X, and let the g-code programmer have complete control of what happens?  Move 
pipe only, torch only, or both, under g-code control.


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Re: [Emc-users] Split X axis - How to go about that?

[andy pugh]

On 17 November 2015 at 20:00, Viesturs Lācis  wrote:

> Why not to treat the chuck motor as another joint of X axis? There
> already are 2 of them (on the gantry), so adding 3rd should be
> straightforward

That ought to work, for the first ever XYZAXX config :-)

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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

>
>>  >One question:  why not make the pipe chuck be a U axis, the torch
>>  >carriage is X, and let the g-code programmer have complete control 
>>of
>>  >what happens?  Move pipe only, torch only, or both, under g-code
>>  >control.
>>
>>
>>  Not sure I understand how to use the U axis. I will be using the
>>  sheetcam rotary plugin to do the gcode. I will have to look at the 
>>usage
>>  of a U axis before I can decide on that.
>
>If you are using CAM it probably makes sense to skip the U axis.
>If you were writing your own G-code the U axis would give you more
>flexibility, but the CAM won't understand it anyway.
>
>Just divide the steps per mm for X in half, and send the X steps to 
>both
>gantry and pipe chuck motors using HAL.  Also send X direction to both
>motors, and invert one so they travel in opposite directions.  Use HAL
>logic (in the base thread) to turn off steps to each motor when that 
>motor
>hits its home switch (only while homing), and to send a composite home
>switch signal to LinuxCNC when both motors have hit their home 
>switches.
>
>If you are generating step pulses in hardware (Mesa, Pico, or other) 
>then
>things get a little more interesting.  More like a servo system, still 
>doable
>but the approach is a little different.
>
The step generation is with software so this approach seems to be the 
thing to do.
Thanks a lot John you have been a great help. I will report back when 
the machine is running.

>
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>   jmkasun...@fastmail.fm
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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

>2015-11-17 21:54 GMT+02:00 John Kasunich :
>>  Just divide the steps per mm for X in half, and send the X steps to 
>>both
>>  gantry and pipe chuck motors using HAL.  Also send X direction to 
>>both
>>  motors, and invert one so they travel in opposite directions.  Use 
>>HAL
>>  logic (in the base thread) to turn off steps to each motor when that 
>>motor
>>  hits its home switch (only while homing), and to send a composite 
>>home
>>  switch signal to LinuxCNC when both motors have hit their home 
>>switches.
>
>Why not to treat the chuck motor as another joint of X axis? There
>already are 2 of them (on the gantry), so adding 3rd should be
>straightforward - that allows homing the chuck to its own switch
>without any additional hassle in HAL or whatever.
>
I probably dont have an idea of how that works. I am not good with 
joints mode.

>Viesturs
>
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Re: [Emc-users] Split X axis - How to go about that?

[Marius Liebenberg]

>2015-11-17 22:23 GMT+02:00 Marius Liebenberg :
>>>Why not to treat the chuck motor as another joint of X axis? There
>>>already are 2 of them (on the gantry), so adding 3rd should be
>>>straightforward - that allows homing the chuck to its own switch
>>>without any additional hassle in HAL or whatever.
>>>
>>  I probably dont have an idea of how that works. I am not good with
>>  joints mode.
>
>You already have 2 joints assigned to X axis on the gantry. Or am I
>missing something? So I think that adding 3d joint to the same X axis
>in HAL should be trivial.
>
No I am using trivial kinematics so there is only one joint for X axis. 
The other side is slaved. So not running in joint mode. I found that 
trivial kinematics is better for gantry systems.


>Viesturs
>
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