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sml2010
 Post subject: rotary axis
PostPosted: Fri Sep 09, 2011 5:31 am 
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Hi


Does the fourth or fifth axis have reference point?
Does the rotary axis need go to reference point when turn on the cnc machine?


Thank you
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Mid Day Machining
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 10:04 am 
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Yes it does. Otherwise it doesn't know where it is. It's just like the X,Y and Z axis. If you don't home them, they don't know where they are.

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Bill Shields
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 11:16 am 
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unless you are using an absolute encoder
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Mid Day Machining
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 12:44 pm 
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Bill Shields wrote:
unless you are using an absolute encoder


If you don't reference the axis, how does it know where it is?

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Bill Shields
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 12:58 pm 
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that is why it is called an ABSOLUTE encoder.

It always wakes up smart, knowing exactly where it is relative to reference zero.

Honest.... :o
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DeanQ
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 10:56 pm 
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Quote:
Does the fourth or fifth axis have reference point?
Does the rotary axis need go to reference point when turn on the cnc machine?

Well, kinda sorta. You zero your rotary out like you do all of your other axis as referenced to you rpart. It doesn't "require" a home limit, but you can incorporate one.
Dean
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Mid Day Machining
 Post subject: Re: rotary axis
PostPosted: Fri Sep 09, 2011 11:24 pm 
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The X, Y and Z axis have absolute encoders as well and they still need to be zeroed when you turn the machine on in the morning so they know where they are.

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Bruce_Mowbray
 Post subject: Re: rotary axis
PostPosted: Sat Sep 10, 2011 6:28 am 
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Correct me if I'm wrong. I thought an absolute encoder knows where its own zero is (within one revolution). The machine must be brought home (to a limit switch type device) to within one encoder revolution of the machine home, then the encoder takes over to find it's own home and the machine control sets this to the axis home position. The Haas rotary axis I used worked the same. When I turned it on, it would look for it's home by rotating slowly. Whenever I powered up the rotary unit, it moved close to the home zero on the axis, the unit would advance slowly and stop when the axis was at it's true "home zero point" and the readout would register at 0.000. I didn't have a choice in this matter. The unit went through an automatic start up procedure before I could use it.

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Mid Day Machining
 Post subject: Re: rotary axis
PostPosted: Sat Sep 10, 2011 7:19 am 
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Bruce_Mowbray wrote:
Correct me if I'm wrong. I thought an absolute encoder knows where its own zero is (within one revolution). The machine must be brought home (to a limit switch type device) to within one encoder revolution of the machine home, then the encoder takes over to find it's own home and the machine control sets this to the axis home position. The Haas rotary axis I used worked the same. When I turned it on, it would look for it's home by rotating slowly. Whenever I powered up the rotary unit, it moved close to the home zero on the axis, the unit would advance slowly and stop when the axis was at it's true "home zero point" and the readout would register at 0.000. I didn't have a choice in this matter. The unit went through an automatic start up procedure before I could use it.


"EXACTLY". Otherwise, how does it know where it is. Once it has been sent to a HOME position, then you can lie to it and tell it a new zero position in your G54 work shift.

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Bill Shields
 Post subject: Re: rotary axis
PostPosted: Sat Sep 10, 2011 8:01 am 
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you are both correct (as am I), but you are missing the big picture here.

for a tool changer, since the carousel only rotates 360 degrees (in this case), having an ABSOLUTE encoder on it that knows where it is relative to reference zero is all that is needed. No need to home on power up.

Capice?
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DeanQ
 Post subject: Re: rotary axis
PostPosted: Sat Sep 10, 2011 11:32 am 
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The OP posed the original questions:
Quote:
Does the fourth or fifth axis have reference point?
Does the rotary axis need go to reference point when turn on the cnc machine?

and somehow got side tracked into tool changers.

Quote:
Bruce_Mowbray wrote:
Correct me if I'm wrong. I thought an absolute encoder knows where its own zero is (within one revolution). The machine must be brought home (to a limit switch type device) to within one encoder revolution of the machine home, then the encoder takes over to find it's own home and the machine control sets this to the axis home position. The Haas rotary axis I used worked the same. When I turned it on, it would look for it's home by rotating slowly. Whenever I powered up the rotary unit, it moved close to the home zero on the axis, the unit would advance slowly and stop when the axis was at it's true "home zero point" and the readout would register at 0.000. I didn't have a choice in this matter. The unit went through an automatic start up procedure before I could use it.


"EXACTLY". Otherwise, how does it know where it is. Once it has been sent to a HOME position, then you can lie to it and tell it a new zero position in your G54 work shift.

Correct! If you want to have repeatability the next time you turn your machine on, it must be 'homed'. I usually do one-offs and don't bother with homing my rotary.
Dean
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Bill Shields
 Post subject: Re: rotary axis
PostPosted: Sun Sep 11, 2011 7:16 am 
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Sorry...same applies to the rotary axes:

If you are using a 4th or 5th axis and you are using ABSOLUTE ENCODERS, you do not need to home / reference.

The same is true if you are using linear ways with ABSOLUTE SCALES - just turn it on and go.
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