ATC senor options

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01 Jun 2019 23:10 #135593 by Ross77
Replied by Ross77 on topic ATC senor options
The pulley remains stationary (axially) and is on a key way to allow the shaft to move in and out. the flange on the pulley is machined to take the encoder disc.


I agree that a machined disk is the way to go. going to test how much depth there is on the edge sensors to provide 3 different radial sectors.

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02 Jun 2019 22:55 #135667 by andypugh
Replied by andypugh on topic ATC senor options
There are some with quite long forks:
uk.rs-online.com/web/p/slotted-optical-switches/1730303/

But you could machine rings pointing in the axial direction, if you really wanted to.
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19 Aug 2019 23:10 #142527 by Ross77
Replied by Ross77 on topic ATC senor options
Slow progress but we are getting there. Went for 3 sensors all in a line and the corresponding Gray scale code holes in the same radius.

We are only using it as a check once in position rather than identifying the position to stop at. works well so far and have it running ok on the bench.

The last issue is the home switch. we have planed to add a 4th sensor purely as a home switch but space is bit of an problem. the sensors a have dual outputs so one option is to feed the second O/P's into a 3input NAND gate and generate a home signal for tool position 1 (all On) Does that sound like a good idea or overkill and it could be done in classic ladder of similar to generate the home signal?

Or any other ideas that I have missed, problem is getting it to work on Linux and Mach3, cheers
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20 Aug 2019 10:37 #142573 by andypugh
Replied by andypugh on topic ATC senor options
I think that a 4th "strobe" signal to indicate that the disc was in a valid position would have been a good idea. With the current arrangement it is hard to tell the difference between 001 and (for example) 111 that is just coming in to position. (Also, in this application there isn't really much point using Gray-code, but neither does it do any harm).

Without a strobe I would say that you do need to synthesise a home signal, and the all-on position does seem like a good way to do that.

For the LinuxCNC application I would not bother with any external circuitry, do it in HAL or inside the component that controls the changer.

I don't think that the LinuxCNC "carousel" component can work with this encoder style, as it looks like there are times as the holes move in to place where (for example) the bit2 hole is in front of the bit0 sensor?

If this isn't the case then it probably can be made to work. Are the forks deep enough that the holes can be drilled on three different radii so that each sensor only ever sees its own hole? if that can be done then the strobe signal can be synthesised in HAL from "NOT all off".

Thinking about this, it would probably be good to add a new parameter to the carousel called something like "ignore-zero" for systems like yours, where if no sensors are active the position feedback is ignore (as when strobe is not set) . I don't think it is too late to add this for the 2.8 release.

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20 Aug 2019 16:52 #142621 by Mike_Eitel
Replied by Mike_Eitel on topic ATC senor options
Can't he use LUT5 in hal?

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20 Aug 2019 17:35 #142628 by andypugh
Replied by andypugh on topic ATC senor options
Yes but a config that only needs to configure carousel would allow the changer to be handled by a standalone HAL file that won't confligt with existing loadrt and addf statements

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20 Aug 2019 20:06 #142641 by Ross77
Replied by Ross77 on topic ATC senor options

I think that a 4th "strobe" signal to indicate that the disc was in a valid position would have been a good idea. With the current arrangement it is hard to tell the difference between 001 and (for example) 111 that is just coming in to position. (Also, in this application there isn't really much point using Gray-code, but neither does it do any harm).


The index sensor was going to be a single slot for accurate homing, are you talking about a 4th bit of grey logic to confirm position?

If this isn't the case then it probably can be made to work. Are the forks deep enough that the holes can be drilled on three different radii so that each sensor only ever sees its own hole? if that can be done then the strobe signal can be synthesised in HAL from "NOT all off".


Certainly an option that we are looking at but will be tight on space.

Thinking about this, it would probably be good to add a new parameter to the carousel called something like "ignore-zero" for systems like yours, where if no sensors are active the position feedback is ignore (as when strobe is not set) . I don't think it is too late to add this for the 2.8 release.


So would that work with our current config?

Yes but a config that only needs to configure carousel would allow the changer to be handled by a standalone HAL file that won't confligt with existing loadrt and addf statements


More research then, I'll have to look at carousel

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20 Aug 2019 20:57 #142644 by andypugh
Replied by andypugh on topic ATC senor options

Ross77 wrote: The index sensor was going to be a single slot for accurate homing, are you talking about a 4th bit of grey logic to confirm position?

Yes. If you had that then there would be no need to home, the system would know where the disc was any time that it was in a valid position. That would require a slot at each position, though.

Thinking about this, it would probably be good to add a new parameter to the carousel called something like "ignore-zero" for systems like yours, where if no sensors are active the position feedback is ignore (as when strobe is not set) . I don't think it is too late to add this for the 2.8 release.


So would that work with our current config?[/quote]

Not if you can have the disc part-way aligned with a sensor active. You either need no sensors active if out of position, or a strobe to say when the disc is in-position.

Much smaller slot detectors exist: uk.rs-online.com/web/p/slotted-optical-switches/6666511/ is almost certainly _too_ small but would potentially work nicely with a 3D-printed target disc: a360.co/2ZpE9sM
(That design is actually for a slightly bigger version with a 3mm slot width, and is binary coded.)

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20 Aug 2019 21:54 #142648 by Ross77
Replied by Ross77 on topic ATC senor options
That's a pretty neat solution, I suppose it really needs the sensors on a PCB for alignments, compactness. and to add the transistors to boost to 24v output.

There is an element of testing needed for the whole ATC so a quick-ish fix would be good in case we need to redesign any other parts

If I can get out current 3 sensor arrangement to work on 3 separate radi then could we get that to work with Carousel and then rework the sensors later?

I also see that carousel is for dc motors with Geneva gears, is it easy to modify the code for stepper motors?

At the moment we have it set up as a rotary axis and use absolute G and M code commands (within the macro) to open the air cylinder turn to the called tool position, works well but is hack of the Denford ATC macro for Mach 3. I probably need to start from scratch

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20 Aug 2019 22:36 #142652 by andypugh
Replied by andypugh on topic ATC senor options

Ross77 wrote: That's a pretty neat solution, I suppose it really needs the sensors on a PCB for alignments, compactness. and to add the transistors to boost to 24v output.

Yes, but then a batch of 10 PCBs costs $5 from China:
www.seeedstudio.com/fusion_pcb.html


If I can get out current 3 sensor arrangement to work on 3 separate radi then could we get that to work with Carousel and then rework the sensors later?

Yes, I think so.


I also see that carousel is for dc motors with Geneva gears, is it easy to modify the code for stepper motors?

Take a look at the enhanced 2.8 version of "carousel", it has a lot more pins and can be connected directly to a velocity-mode step-generator:
linuxcnc.org/docs/2.8/html/man/man9/carousel.9.html
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