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Add Z-Axis to my machine

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30 Jan 2019 14:45 #125292 by andypugh
Replied by andypugh on topic Add Z-Axis to my machine

Andy do they do some trickery with the electronics because my current Parker Motion motor that I'm adding to my Z says 1000ppr in the literature but it gives 4000 ppr on ORES/ERES in the software settings EPROM. So maybe that would be the case with these new encoders as well? 4x the stated PPR?

Quadrature gives you 4 x the slots as counts, as there are 4 events per slot as it goes round. The Amazon encoders might have 150 slots for 600 counts or 600 slots for 2400 counts.


So my dilemma is this ...I can't really rip the encoder off of this parker servo so I'd have to scrap it completely if I wanted to get a servo with a resolver.

Your current resolvers seem to be mounted on the screws rather than on the servo?


I guess I just feel like I'd be going backwards at this point to go resolver.

Resolvers have gone out of fashio partly as they are harder to interface with digital electronics and partly as they cost a lot more to make than encoders But they are in many ways superior to encoders (they are a lot tougher, are pretty much insensitive to contamination and there is nothing to age / wear out)


One last thing is one day in the future (hopefully not so far) I'd love to rip that 3-phase off of the top of my mill and replace all that crap up there with a direct drive 1.5Kw servo motor. That would let me do rigid tapping


Add an encoder / resolver to your spindle and you can do rigid tapping today. LinuxCNC does not need a servo spindle for rigid tapping, just a spindle that LinuxCNC can start and reverse.

Why have you given up on the idea of connecting an encoder to the 7i42? It just needs a new firmware and PCW can probably be persuaded to make you one.

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30 Jan 2019 15:01 #125295 by hatch789
Replied by hatch789 on topic Add Z-Axis to my machine
Yes my current resolvers are mounted on screws not on the servo itself. I was talking about my new Parker Motion servo that I want to use for Z. That one has the encoder on the back as part of the unit and there's no way I am removing it to put a resolver on. So I'd have to just scrap the idea of using that one altogether if I want to use a resolver with my Z. It is a several thousand dollar servo and drive. Plus I have 4 more of them!! :) Ideas ideas ideas.

Thank you for the explanation on resolvers vs encoders. I didn't realize they were in many ways superior so that is kinda cool. But it still leaves me with 2 different setups requiring a lot of fudging around.

The reason I am not going after the 7i42TA idea was you said it can handle a few KHz signal but then I learned my Parker server runs at 4000pps and a normal slow move is in the 20 - 30 rps range effectively pushing my 7i42 way too fast to track. That would be 80 - 120Khz it would need to read. So that's why I started thinking OK I'll switch to a 7i48 card and go with encoders everywhere.

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30 Jan 2019 15:12 #125296 by andypugh
Replied by andypugh on topic Add Z-Axis to my machine

The reason I am not going after the 7i42TA idea was you said it can handle a few KHz signal but then I learned my Parker server runs at 4000pps and a normal slow move is in the 20 - 30 rps range effectively pushing my 7i42 way too fast to track. That would be 80 - 120Khz it would need to read.


Sorry, perhaps I was unclear.

7i42 + GPIO into HAL _software_ encoder counter is limited to a few kHz.
7i42 + special bitfile for hardware encoder counter = limited to a few MHz.

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30 Jan 2019 15:13 #125297 by Todd Zuercher
Replied by Todd Zuercher on topic Add Z-Axis to my machine
So did your old system have any Z position feedback?

Does your Parker servo do position control? If so you could always just control it with step/dir. and either have no feedback to Linuxcnc or keep what ever feedback you had before on the Z.

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30 Jan 2019 15:28 #125300 by hatch789
Replied by hatch789 on topic Add Z-Axis to my machine
Andy thank you for clarifying ...I didn't realize with a new bitfile that it could read a lot more. hmmm --But I still need to get a custom bitfile and I've never made one before. I did at least download the software for using it on Windows to make a bitfile.

Todd, the parker servo has torque mode, velocity mode, Position / Step mode. It's a GV-L3E drive so it's pretty high-tech. It is 20 year old tech but still nice. I have SM-233AE motors. So I have 5 servos w/ encoders and 5 drives. That's why I wanted to use what I had which was nice and bonus ...it's free.

I do see encoders on e-bay with ABZ and I could get them (from china) but I'll be waiting 2 weeks or more I bet. :( sucks. Anyone know of a decent place here domestically that won't cost me hundreds of dollars to do this?

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30 Jan 2019 16:41 #125305 by OT-CNC
Replied by OT-CNC on topic Add Z-Axis to my machine

I do see encoders on e-bay with ABZ and I could get them (from china) but I'll be waiting 2 weeks or more I bet. :( sucks. Anyone know of a decent place here domestically that won't cost me hundreds of dollars to do this?


US Digital. You can custom configure their encoders. I have their E5. I would recommend buying their wiring with connector when ordering.

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30 Jan 2019 16:43 #125307 by hatch789
Replied by hatch789 on topic Add Z-Axis to my machine
are they reasonable rates for someone with a limited budget? I just need a reliable unit I don't need crazy awesome! :)

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30 Jan 2019 16:53 #125309 by OT-CNC
Replied by OT-CNC on topic Add Z-Axis to my machine

are they reasonable rates for someone with a limited budget? I just need a reliable unit I don't need crazy awesome! :)


Look at their website. The pricing is published....

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30 Jan 2019 17:43 #125313 by OT-CNC
Replied by OT-CNC on topic Add Z-Axis to my machine

So my dilemma is this ...I can't really rip the encoder off of this parker servo so I'd have to scrap it completely if I wanted to get a servo with a resolver. Plus finding the resolvers seems to be a pain because they are older tech. Yes I see them on e-bay but you'd really recommend putting resolvers on new servos just to keep resolvers?


I just looked at your youtube vid of the z servo motor fitted to the knee. Where did you plan on mounting the encoder? Why not get a linear encoder mounted to the knee if you're really set on moving the knee? Read that into linuxcnc. Leave the parker and the x and y as is since it's working.

I'm not familiar with your mill but I assume the knee has backlash so you will be better off reading the position directly off the knee via linear encoder.

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30 Jan 2019 18:23 #125314 by OT-CNC
Replied by OT-CNC on topic Add Z-Axis to my machine

Add an encoder / resolver to your spindle and you can do rigid tapping today. LinuxCNC does not need a servo spindle for rigid tapping, just a spindle that LinuxCNC can start and reverse.


Andy,
Do you have a recommendation on relay/contactor units that would work well? I have been entertaining the idea of skipping the VFD for my Bridgeport mill as I really only need FW/RW. I have seen motor control units (contactors) that have a safety built in so you can't active FW/RW at the same time. Do you know of a "modern" equivalent in say a SSRs that can handle 2hp 3ph 230v start up current and cost less than a VFD for FW/RW switching? Is there an easy way to add a delay between the FW/RW switching in the config (other than adding dwell in g code) for allowing the motor to coast down before changing direction?
Would a breaking resistor be necessary for repeated tapping if stopping the motor quickly is not of concern? I think my motor is a non cap motor so blowing a cap with frequent start/stop is probably less of an issue.

I don't want to hijack the OP's thread. Let me know if this needs moving.

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