ATC senor options

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30 May 2019 23:02 #135436 by Ross77
ATC senor options was created by Ross77
Myself and a friend are currently building an 8 station ATC for our lathes. its uses a Hirth style connector instead of the ratchet and pawl so all the holding force is managed by that.


The tool plate will be rotated by a stepper motor so in theory it just needs an initial index and then move a set amount of steps to the desired tool position. we have based it on the Denford ATC which uses a 3 ch greyscale to confirm tool position and my mate wants to copy this design so we can confirm tool position at the end of the change sequence. Whilst its not a massive amount of work Im not sure it is required when the tool plate is self centring and using a stepper motor for position.


Are there any other ways to confirm tool position or it complete over kill in use?

I have a video but can seem to add it

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31 May 2019 06:50 #135448 by pl7i92
Replied by pl7i92 on topic ATC senor options
if the stepper is powerful 4-8Nm y<ou can go with that
there is a BCD component that workes with CARUSELL you can use to ident the position
but no need at all
it will work as you like it without anything

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31 May 2019 12:50 #135463 by andypugh
Replied by andypugh on topic ATC senor options

Ross77 wrote: The tool plate will be rotated by a stepper motor so in theory it just needs an initial index and then move a set amount of steps to the desired tool position. we have based it on the Denford ATC which uses a 3 ch greyscale to confirm tool position


You could use just a single home position sensor, but the added complexity to add a gray-scale (and strobe, ideally) isn't huge, and adds a fair but more robustness to the system.

As far as I can remember the linuxcnc "carousel" component needs at least an index pulse for each tool and a home sensor for tool 1. So if you reduce complexity in the hardware you will be adding some in HAL to deal with your system.

I imagine that your reluctance to add multiple sensors is due to using a parallel port and being short of pins?

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31 May 2019 17:09 #135488 by Ross77
Replied by Ross77 on topic ATC senor options

if the stepper is powerful 4-8Nm y<ou can go with that


The tool plate spins freely when open so power wont be an issue, plan to use a 2nm stepper.

You could use just a single home position sensor, but the added complexity to add a gray-scale (and strobe, ideally) isn't huge, and adds a fair but more robustness to the system



yes I agree its not a massive amount of work but is bit of a faf making the grayscale disk and then aligning the 3 sensors. I would prefer an edge detected slot disc but I don't think that would work for grey scale. could go quadrature with 2 sensors but then then needs a processor to keep count etc.


I imagine that your reluctance to add multiple sensors is due to using a parallel port and being short of pins?



No not at all, I have plenty of I/O, it just seemed a bit old school with sticky tape an IR sensors, I can see the tape peeling off over time and causing problems. I mainly want to see if they was another way to do it or if it was over kill as most of the stepper driven atcs don't have sensors.

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31 May 2019 17:57 #135492 by andypugh
Replied by andypugh on topic ATC senor options

Ross77 wrote: yes I agree its not a massive amount of work but is bit of a faf making the grayscale disk and then aligning the 3 sensors. I would prefer an edge detected slot disc but I don't think that would work for grey scale.

Reflective sensors can work pretty well at detecting holes, especially if whatever is on the other side is an angled face.
(Oh, and in this case it is "Gray" scale, named after a chap)

No not at all, I have plenty of I/O, it just seemed a bit old school with sticky tape an IR sensors,

The Orac seems to use a disc with marker pen tracks on it. Though that might not have been original.

You can certainly use forked transmissive sensors working on two different radii and an edge-slotted disc, with the index being a longer slot.

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01 Jun 2019 10:00 #135553 by Ross77
Replied by Ross77 on topic ATC senor options
Ok Thanks, that's a big help.

I like the idea of slots with a reflective disc behind, seems a bit more robust. The carousel option would be ok for me but my mate uses Mach 3 so we need non software option.

I've ordered up a few variations of sensors so we can trail each one.

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01 Jun 2019 16:32 #135578 by andypugh
Replied by andypugh on topic ATC senor options

Ross77 wrote: The carousel option would be ok for me but my mate uses Mach 3


It might be simpler to change friends :-)

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01 Jun 2019 16:52 #135579 by pl7i92
Replied by pl7i92 on topic ATC senor options
i agree to andy
change your friend and get off MS
use LinuxCnc and you got far more options
plenty of Help

you can also use a Encoder 1000steps/rev
to see where you in place
make the ATC only 360 deg and you are in place with a simple counter
the NGC that controls your toolchange will then have a error routine that tels you how many steps you are off
but you can get microstepping to fit it perfect
1000ppr is in Linuxcnc 4000pulses so you got plenty of space to your rotation

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01 Jun 2019 21:09 #135584 by Ross77
Replied by Ross77 on topic ATC senor options

It might be simpler to change friends

Haha, seems a little harsh! especially as he has done 80% of the machining. :laugh:

i agree to andy change your friend and get off MS use LinuxCnc and you got far more options plenty of Help


Im already using Linux, if he didn't have the CSlabs controller I think he probably would change. Ive got him to try Linux and mesa on the nova mill we are upgrading, so its a start. :0)

you can also use a Encoder 1000steps/rev
to see where you in place
make the ATC only 360 deg and you are in place with a simple counter
the NGC that controls your toolchange will then have a error routine that tels you how many steps you are off
but you can get microstepping to fit it perfect
1000ppr is in Linuxcnc 4000pulses so you got plenty of space to your rotation



I did consider that but we cant get an encoder on the main shaft and the stepper is on a 3:1 ratio so the index wouldn't work. The Hirth coupling is self centring so the stepper doesn't have to move perfectly to the desired position. its more just to confirm it is in the correct tool before the cycle starts.
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01 Jun 2019 21:54 #135588 by andypugh
Replied by andypugh on topic ATC senor options
Embed a hall sensor in each detente, and have a small magnet embedded in one tooth.

Or, a small webcam and OCR reading numbers directly.

For robustness I think I would prefer proximity sensors and a machined encoder plate. (possibly a pattern machined into the rotating component, but the sensor array would probably have to move in and out with the plate.)
machining a pattern of slots into the shaft might work, and doesn't have the problem that the distance moves when the clamp actuates. The slots move out of alignment with the sensors, but that might not be an insurmountable problem, as you are already in position then.

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