Home to limit switches.

[eman5oh]

I have a 3 axis router with +/- limit switches on each axis and can't seem to get it configured to home and use the limit switches. Is there a way to modify the home macro to disable the limits then use the input for homing and when done turn the limits back on? I have managed to get the home to work if I just set up the home all and use soft limits, it works but would like to make use if the limit switches if something goes wrong.

[ShawnM]

Please post a copy of a current report so we can see how you have your inputs configured. Maybe some pics as well.

There are LIMIT switches and there are HOME switches. These need to be configured correctly in the wizard to work as HOME and LIMIT switches. They are NOT the same. I'm assuming you have a switch at each end of travel? Sounds like you have them together. Pics and a report would help us help you. Three home switches are all you need. The soft limits work flawlessly for travel limits.

[cncsnw]

Soft limits work flawlessly, as long as all the other components of the system, plus the operator, work flawlessly.

If, on the other hand, the operator jogs too fast in the wrong direction before homing the machine, then a machine without limit switches can crash badly.

Or if -- as often happens with open-loop control -- the control has dropped steps and lost position since it was homed, then a machine without limit switches can also crash badly.

Or if, as happens with both open-loop and closed-loop control, something has slipped in the drive train and the machine has lost position, then a machine without limit switches can also crash.

Limit switches provide an extra layer of protection, in case of operator error or loss of position.

Omitting limit switches, and wiring all home switches to a single input, were compromises that were made to work around the original Acorn's critical shortage of PLC inputs.

Given the choice, a reasonable installer would wire switches at each end of each axis to separate PLC inputs (i.e. a total of six switches, on six inputs, for a 3-axis machine). If you do that, then each axis can home in whatever direction is appropriate, using the limit switch in that direction as the home switch. That is how closed-loop Centroid controls have generally worked since at least 1993. That could be done on an Acorn, if you were to use an I/O expansion board so that you have enough inputs.

Unfortunately, as far as I can tell, the Acorn Wizard does not have any canned configuration for a home/limit switch on one end of one axis. It only allows for axis- and direction-specific switches that are limits, and not used for homing. You can set your switches up this way on the Machine Configuration -> Motor Parameters table, but you cannot do it through the Wizard.

As Shawn suggested, if you were to post a Report from your system, then we could see what inputs you have used, and make more informed suggestions.

[ShawnM]

Soft limits work flawlessly, as long as all the other components of the system, plus the operator, work flawlessly.

If, on the other hand, the operator jogs too fast in the wrong direction before homing the machine, then a machine without limit switches can crash badly.

That is correct Marc and I'm assuming that the operators out there are just slightly smarter than the machine. I love the soft limits and it frees up all those inputs for other gadgets and remote buttons.

Hopefully eman5oh will post a report AND some pics so we can get this sorted out for him.

[eman5oh]

Hi All,

I have attached a report and current picture of the machine as well as a google photos link to more pics of the router. I started building this over 10 years ago and am just now getting around to finishing it, kids and building a house got in the way... I certainly would do thinks differently if starting today. In any case I would like to have the limit switches act as a home switches as well. I can wire it however needed to make it function as I am still building the control box. I also have a Bridgeport Boss 5 mill that I retrofit Linux CNC controls on, the Bridgeport has a single limit switches on the X and Y with the Z having both + and - limits but no home switches on any of the axes. I have it configured to home to the limit switches on all three axes, I was hoping to do the same on the Acorn.

https://photos.app.goo.gl/RgRD8y274nVZPFT27

[ShawnM]

The machine will HOME to the HOME switches, not limit switches. There's a difference between HOME switches and LIMIT switches. Try not to confuse the two. You have input 1 set up as home all so the switch(s) wired to that input are your HOME switches. The homing sequence is set up in the wizard.

You don't have any inputs setup for limit switches.

I see no pics of your home switches or limit switches.

The biggest issue I see is using a laptop with a USB to ethernet adaptor. This is not preferred and you cannot get support for CNC12 using a laptop let alone a laptop using a USB to ethernet adaptor. You'll have issues with this along with communication errors.

Good luck with your build.

[eman5oh]

I have attached a picture of the limits switches, they are all the same plunger style switches that truely are end of travel limits. When one is hit there is about .050 of travel left before the axis hard stops and stalls the motor. I wish I had a better setup for the limits but it is what it has. So I understand this correctly Acorn can NOT have a switch perform as both a home and a limit? If so that is a bummer, I was thinking of trying an Acorn on my Boss Mill and that would have an issue as well. I was hoping Acorn would have something like Home_Ignore_Limits functions that I am using with Linux CNC on my Mill, works perfectly. As for the laptop, I have a NUC I5 that will be running the router with, just some light testing with the laptop.

https://linuxcnc.org/docs/2.6/html/conf ... oming.html

[ShawnM]

You can set up the inputs to be "HomeLimits" but you have to wire each switch to it's own input. This option is in the input section in the wizard. Apparently you now have the 3 of those switches wired together in series or parallel, as I don't know if they are NO or NC, and wired to "HomeAll" on input 1. NC switches are ALWAYS preferred. All you have to do now is go in and setup your soft limits and you are done. If you want to rewire all the switches to use individual inputs you can but this wouldn't make any sense in my opinion. Wire the opposite end switches the same way as limit switches to a single input set to "limit all".

This is assuming that you have 3 switches at one end of travel and 3 switches at the other end of travel on each axis.

I'd still setup your soft limits as a buffer and safety backup to within about 1/8" of those switches.

Please explain a little better as to what you are trying to achieve?

[eman5oh]

Shawn,

Thank you for taking the time to help me with this! I currently have all six limit switches wired in series, they are normally closed switches. My goal is to have three of the switches, one X one Y and one Z act as both a limit and a home switch and the other three switches act as just limit switches. Can I put the three in series and set them to "HomeLimits" on input 1 and take the other 3 wire them in series and set them to "Limits All" on input 2 or do I need to wire them individually to X- Y- Z+ Limits each to an input?

[ShawnM]

You can't wire all 6 together, that's your issue.

You can wire three in series as home switches to input 1 set as "HomeAll" and wire the other three in series to input 2 and set it as "LimitAll". You can then setup your soft limits to be just inside these switches as an added backup.