M39 Spindle encoder getting crazy numbers


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Thread: M39 Spindle encoder getting crazy numbers

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    Default M39 Spindle encoder getting crazy numbers

    I have been working on putting a spindle encoder on an old Kasuga knee mill running an M39 control with version CNC11-D for CNC10 V.2.72 (linux). The hardware side went together easy but now that I have the encoder hooked up the RPM is readying about 20x higher than it should. The encoder is an Omron E6B2-CWZ1X quadrature 2000 P/R so I set parameter 34 to 8000. If I set the count to around 160000, yes 160k, the rpm displayed is about what I see with the tach.

    I originally thought it was the encoder so I swapped it. I then thought maybe it was the cable extension, so I removed it. Still no joy. If I only hook up the index it does appear to count correctly but I haven't checked with the tach to know how close it is or isn't.

    I understand it very likely could be the style of encoder I selected and/or the fact it's a Omron knockoff from Ebay. I did test it on the scope and all A, B, & Z channels are counting.

    What kind of encoder should I use? Or do I simply have something wired wrong?

    My pinout is:
    Pin 1 N/C
    Pin 2 Com
    Pin 3 -Z
    Pin 4 -A
    Pin 5 -B
    Pin 6 Z
    Pin 7 A
    Pin 8 B
    Pin 9 +5V

    Here's a couple photos of my 1:1 adapter. The belt I'm using is a MXL. The adapter and pulleys appear to drive the encoder well with no issues so far. There was a spacer below the power drawbar so it was trivial to replace the spacer plate with the adapter of the same thickness. Just enough to sneak in a belt without needing to alter the drawbar.

    M39 Spindle encoder getting crazy numbers-encoder-mount-v27-pngM39 Spindle encoder getting crazy numbers-img-3606-jpgM39 Spindle encoder getting crazy numbers-img-3674-jpg

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    Gold Member Jim Dawson's Avatar
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    Default Re: M39 Spindle encoder getting crazy numbers

    I would say if it reads correctly at 160,000 then why not just use that figure? It could be that the original encoder was much lower line count.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: M39 Spindle encoder getting crazy numbers

    Quote Originally Posted by Jim Dawson View Post
    I would say if it reads correctly at 160,000 then why not just use that figure? It could be that the original encoder was much lower line count.
    I've run that way for a few days but I simply cannot figure out why an 8000 count encoder would appear as 160000. When I was checking it with the tach the adjustment was actually closer to 157000 to get a match. This made me suspect noise but even at low rpm, say 100 rpm, it's over counting. I'd be curious to know what make/model encoders others are using on their spindle.



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    Gold Member Jim Dawson's Avatar
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    Default Re: M39 Spindle encoder getting crazy numbers

    I use a 50 line A/B quadrature on my mill, using that one because I had a couple on the shelf. Don't remember the brand, proabaly 20 years old. My lathe has a 1024 line differential quadrature, and again I don't know the brand. Both work just fine. Your Omron should work just fine, as long as you have a clean signal on the scope I would say it's working.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: M39 Spindle encoder getting crazy numbers

    Quote Originally Posted by Jim Dawson View Post
    I use a 50 line A/B quadrature on my mill, using that one because I had a couple on the shelf. Don't remember the brand, proabaly 20 years old. My lathe has a 1024 line differential quadrature, and again I don't know the brand. Both work just fine. Your Omron should work just fine, as long as you have a clean signal on the scope I would say it's working.
    I'm thinking that high count may be saturating the old ISA based card. I poured through the manual and at the it implies encoders back in the day were less than 1024 lines. Good to know an encoder with 50 lines would work. Is your control ISA or PCI? What version?

    Parameter 34 4,096 Sets the counts per revolution (cpr) of the encoder. The encoders so far have been 1024 lines, providing 4096 cpr. If the encoder counts up when the spindle turns CW then the value should be positive. If the encoder counts up when the spindle turns CCW then the value should be negative.




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    Default Re: M39 Spindle encoder getting crazy numbers

    I suspect there is another multiplier parameter somewhere in the control software, such as "spindle pulley ratio" or something like that. Just a wild guess.



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    Default Re: M39 Spindle encoder getting crazy numbers

    Quote Originally Posted by CitizenOfDreams View Post
    I suspect there is another multiplier parameter somewhere in the control software, such as "spindle pulley ratio" or something like that. Just a wild guess.
    That's a good idea. I was thinking the same and just didn't find anything obvious. I've looked at parameters 33, and 65-67.



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    Default Re: M39 Spindle encoder getting crazy numbers

    Quote Originally Posted by forhire View Post
    I'm thinking that high count may be saturating the old ISA based card. I poured through the manual and at the it implies encoders back in the day were less than 1024 lines. Good to know an encoder with 50 lines would work. Is your control ISA or PCI? What version?

    I'm not using a Centroid control. The heart of my system is a Galil DMC-1846 PCI motion controller, good for up to 22 MHz encoder inputs. The older ISA boards were good for 6 MHz as I recall. I assume the Centroid is somewhere in the same range.

    The encoder scaling parameter may have another multiplier hard coded into the system. Maybe 10x or 100x ?

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: M39 Spindle encoder getting crazy numbers

    Quote Originally Posted by Jim Dawson View Post
    I'm not using a Centroid control. The heart of my system is a Galil DMC-1846 PCI motion controller, good for up to 22 MHz encoder inputs. The older ISA boards were good for 6 MHz as I recall. I assume the Centroid is somewhere in the same range. The encoder scaling parameter may have another multiplier hard coded into the system. Maybe 10x or 100x ?
    I haven't found any scaling parameter. I can't imagine it would be hard coded.

    I'm thinking it may be signal voltage. This tech note lists the the high must be greater than 3.5V.
    http://www.centroidcnc.com/dealersup...ploads/280.pdf
    1. Confirm that you encoders meet Centroid signal specifications. Centroid requires
    quadrature, differential line driver encoders that meet the RS422/423 specifications. In
    addition, the “low” signal level must be < .5VDC and the “high” must be >= 3.5VDC.



    The spec sheet from Omron lists the Vo: 2.5 V min. and Vs: 0.5 V max. This matches the spec sheet for the TI RS422 differential driver chip used on this clone. I don't recall what the voltage was when we had it on the scope.

    I wonder what Centroid is thinking. A real RS422 receiver shouldn't care what the voltages are, only the difference between the lines. That is the whole point of using differential signals.

    I guess I need to find an encoder that meets Centroid specifications.



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    Default Re: M39 Spindle encoder getting crazy numbers

    I would put the scope back on the lines and get some good numbers. I would expect to see >4.5V max and <0.5V min for the positive going signal and <-4.5V min and >-0.5V max on the negative going signal. I don't have time right now to connect a scope to an encoder to look at the output, but maybe I could later.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: M39 Spindle encoder getting crazy numbers

    Some more poking around. I found a list of encoders here: Encoders Used on Centroid Controls

    I then looked up one of them, the Quantum Devices QD145, and compared the specs. QD145 Optical Incremental encoder by Quantum Devices, Inc.

    Both the Omron and the Quantum Devices use the same TI AM26LS31 Quadruple Differential Line Driver. The difference is the the QD145 includes an OL7272 High Voltage Line Driver TTL Output to bring the signal back up to 5V.

    Clearly Centroid is expecting TTL signaling rather than LVTTL. The search continues.



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    Default Re: M39 Spindle encoder getting crazy numbers

    What values do you have in Parameter 36 and Parameter 65?

    If you have set bit 4 of Parameter 36, then the control will assume the encoder is on the motor. If the PLC then indicates that the spindle is in low range, CNC10 will multiply the encoder speed by the ratio in Parameter 65 to get the display value.

    However, I think that path can only lead to a lower-than-actual spindle speed reading.

    If you press Emergency Stop, then turn the spindle by hand (say, at around 60 or 120 RPM) is the displayed speed accurate, or does it still count high? Often the VFD is the biggest source of noise and interference.



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M39 Spindle encoder getting crazy numbers

M39 Spindle encoder getting crazy numbers