Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
01 Jun 2014 16:01 #47590
by Skippy1
Spindle Encoder on Motor with 1:1 HTD Belt Drive ? was created by Skippy1
Chaps,
I'm putting a new motor and VFD on my lathe. I understand that I need to put an encoder on the spindle for thread cutting etc. (I'm using a Mesa 5i25 and 7i76 setup).
Anyway, the new (fleabay) Baldor' 'Vector Master' motor has a good A, A-, B, B- and Z encoder on the back end, and I wondered if I could use a timing belt (HTD series or similar) for the spindle drive with a 1:1 ratio, and use the encoder on the motor to tell LinuxCNC where the spindle is.
While I probably won't go down this path, what I was really curious about is - if LinuxCNC had the 'smarts' to cope with a ratio other than 1:1 ?
Cheers, Steve
I'm putting a new motor and VFD on my lathe. I understand that I need to put an encoder on the spindle for thread cutting etc. (I'm using a Mesa 5i25 and 7i76 setup).
Anyway, the new (fleabay) Baldor' 'Vector Master' motor has a good A, A-, B, B- and Z encoder on the back end, and I wondered if I could use a timing belt (HTD series or similar) for the spindle drive with a 1:1 ratio, and use the encoder on the motor to tell LinuxCNC where the spindle is.
While I probably won't go down this path, what I was really curious about is - if LinuxCNC had the 'smarts' to cope with a ratio other than 1:1 ?
Cheers, Steve
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01 Jun 2014 16:31 #47593
by emcPT
Replied by emcPT on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
Yes to both questions
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01 Jun 2014 16:44 #47594
by Skippy1
Replied by Skippy1 on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
OK, now you have my attention. Say hypothetically, I run a 2:1 ratio, with a 60 tooth on the motor and 30 tooth on the spindle, can I configure it to 'see' spindle position every second Z pulse? Likewise, if a ran an obscure ratio like 54 to 36, could Linux still do the required 'maths' to work it out?
Cheers, Steve
Cheers, Steve
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01 Jun 2014 18:03 - 01 Jun 2014 18:06 #47597
by BigJohnT
Replied by BigJohnT on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
Generally you want to use a 1:1 ratio for a spindle encoder as you want the index to be once per revolution. On a mill this is not as critical as a lathe would. To thread on a lathe you have to have only one index per rev.
As for the number of pulses per rev it can be almost anything within reason.
JT
As for the number of pulses per rev it can be almost anything within reason.
JT
Last edit: 01 Jun 2014 18:06 by BigJohnT.
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01 Jun 2014 20:36 - 01 Jun 2014 20:37 #47600
by PCW
Replied by PCW on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
Its possible to mask the index pulse in hardware for cases with 1:2 or 1:3
spindle to encoder ratios.
Its also possible to make a index component that generates the index signal
at any required division ratio, with the limitation that the index position will be lost across linuxCNC sessions (which is probably not too important unless you resume a threading or tapping cycle after shutting down LinuxCNC)
spindle to encoder ratios.
Its also possible to make a index component that generates the index signal
at any required division ratio, with the limitation that the index position will be lost across linuxCNC sessions (which is probably not too important unless you resume a threading or tapping cycle after shutting down LinuxCNC)
Last edit: 01 Jun 2014 20:37 by PCW.
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02 Jun 2014 18:33 #47623
by andypugh
LinuxCNC is happy with any number of counts per rev, so you could use any ratio at all for spindle position tracking.
The fly in the ointment is the index pulse, which needs to be one pulse per spindle revolution. It is possible to fiddle this in the software, but not trivial when you have a hardware encoder counter.
What is quite straightforward is to connect the A and B of the encoder to the 7i76 but to have a separate index sensor on the actual spindle. This could be a hall sensor sensing a magnet, for example. (in fact, it could be the pickup from a bicycle speedo). Alternatively you could use a proximity sensor looking at a keyway on the spindle shaft, or an opto-sensor looking at a flag or a piece of reflective tape on the spindle pulley.
Replied by andypugh on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
While I probably won't go down this path, what I was really curious about is - if LinuxCNC had the 'smarts' to cope with a ratio other than 1:1
LinuxCNC is happy with any number of counts per rev, so you could use any ratio at all for spindle position tracking.
The fly in the ointment is the index pulse, which needs to be one pulse per spindle revolution. It is possible to fiddle this in the software, but not trivial when you have a hardware encoder counter.
What is quite straightforward is to connect the A and B of the encoder to the 7i76 but to have a separate index sensor on the actual spindle. This could be a hall sensor sensing a magnet, for example. (in fact, it could be the pickup from a bicycle speedo). Alternatively you could use a proximity sensor looking at a keyway on the spindle shaft, or an opto-sensor looking at a flag or a piece of reflective tape on the spindle pulley.
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03 Jun 2014 17:03 #47651
by Skippy1
Replied by Skippy1 on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
Thanks guys,
I was considering anything to try and get the encoder off the back of the spindle/head stock and out of sight. (While the lathe will be a conversion, I don't what little bolt-on bits hanging off it.) It sounds like it is possible, especially if I put a separate simple Z index pickup inside the head stock. That would allow me to run whatever ration between the motor and spindle I want too.
Thanks, Steve
PS - I should have bought a CHNC instead of a HC, and everything would have been much neater.
I was considering anything to try and get the encoder off the back of the spindle/head stock and out of sight. (While the lathe will be a conversion, I don't what little bolt-on bits hanging off it.) It sounds like it is possible, especially if I put a separate simple Z index pickup inside the head stock. That would allow me to run whatever ration between the motor and spindle I want too.
Thanks, Steve
PS - I should have bought a CHNC instead of a HC, and everything would have been much neater.
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03 Jun 2014 18:15 #47652
by BigJohnT
Replied by BigJohnT on topic Spindle Encoder on Motor with 1:1 HTD Belt Drive ?
Yea the CHNC spindle encoder is built into the spindle.
Here is my CHNC conversion:
gnipsel.com/shop/hardinge/hardinge.xhtml
JT
Here is my CHNC conversion:
gnipsel.com/shop/hardinge/hardinge.xhtml
JT
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