Home all and limit all

All things related to the Centroid Acorn CNC Controller

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cryptonym
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Home all and limit all

Post by cryptonym »

I am setting up my Acorn on a onefinity with prox sensors on home and limits on other ends. All work fine. In testing, I notice that if I trip a home sensor it doesn't alert as a limit problem. I originally thought all the homes served as both home AND physical limits, but it wasn't working that way.

I've never seen anything in the wizard and was poking around in config. I'm away from it now, but either the motor or jog screen had fields to set the +/- limits and +/- homes. They were filled with the respective home all and limit all I configured in the wizard. I manually changed the limit position on the home end to use the home all value instead of limit all. This meant that the home end has both a limit and home value set to the home all input. Now if I trip any sensor I get the limit trip alert. Homing works normally.

But, if I run the wizard, save and restart, it has set it back to the "limits are limits and homes are just homes" value.

My reason wanting this is in case it would hang up and lose location. The machine uses open loop steppers.

Am I doing something incorrectly? Might be nice if this was exposed in the wizard, or if it didn't erase the work.
cnckeith
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Re: Home all and limit all

Post by cnckeith »

post a fresh report.zip so we can see your cnc configuration settings and choices.

you have many choices for home and limit switch configuration and operation.

home switch.. all it does is home.

limit switch.. all it does is stop the machine when triggered

combination switch "home_limit" does both jobs, acts as home switch while in the home program, then acts as limit switch when not running the home program.

all the choices are found in the Wizard. simply drag and drop what you want where and the wizard will set those up for you and create a home program to match. easy peasy
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
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TopQuarkDoc
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Re: Home all and limit all

Post by TopQuarkDoc »

Amazing coincidence as I was just getting ready to ask this, and I instead found this very recent post.

What is the result if one uses the the same switch for "home" and "limit"? Electrically meaning all three (mill) axis switches are in series (for "HomeAll") with one end of the string connected to common and the other to the input defined for "HomeAll" and then the "HoemeAll" input is jumpered to the input defined for "LimitAll". Assuming the axis will home properly, what does the Acorn do if the switch is tripped after homing? Will it then act as a limit switch?

Yeah Keith, after 18 months of "paralysis by analysis", I finally did all the mechanical work to mount everything for the conversion. Mostly finished the schematics, and I'm now laying out the wiring.

Thanks for the time.
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Re: Home all and limit all

Post by cnckeith »

Centroid CNC12 software supports a wide variety of Home and Limit input combinations and configuration. Centroid has provided the tools so that the integrator can configure and use the machine’s home and limit switches any way he likes. These tools are: The CNC12 PLC program, CNC12 Macro programming, CNC12 configuration menus.


The Acorn and AcornSix Wizard provides the user with home and limit switch configuration with auto home program generation so the users does not need to learn how to Edit a PLC program, CNC Macro programming or use the CNC12 configuration menus.

The Wizard provides easy drag and drop and click method to configure a wide variety of Home and Limit combinations.

Centroid’s #1 recommended home switch configuration is to use one home switch per each axis of the machine tool. Wire all Home switches into one input defined as “HomeAll” and use Software Travel Limits to control the travel limits of the machine tool on both the plus and minus side of each axis.

Centroid’s #2 recommended home switch configuration is to use one home switch per each axis of the machine tool. Wire all Home switches into one input defined as “HomeAll” and use Software Travel Limits to control the travel limits of the machine tool on both the plus and minus side of each axis. And use Limit switches on each side of each axis of the machine tool, wire them all into one input “LimitAll” as seen in schematic #14954 https://www.centroidcnc.com/dealersuppo ... 954.r5.pdf


I will describe here how to use Home and Limit switches with the Acorn/AcornSix Wizard.
So, lets start and define what a Home Switch is and what it does and what a Limit Switch is and what it does.

Home Switch:

- A switch used to define the location of the machine home position.
- Home switches are used to ‘remember’ the machine home position, machine work envelope and part zero position after a machine tool power cycle.
- Home switches are only active during the home program (cncm.hom, cnct.hom).
- Home switches are not limit switches.
- Home switches are ignored during regular CNC control operation
- The more accurate the home switches the more accurate the remembering of the part zero position is after a power cycle.
- Home switches should be “Normally Closed”. “Normally Closed” = Closed when NOT tripped.
- Home switches can be wired to individual inputs or all switches wired into one input called “HomeAll” (to save on inputs)
- Home switches should be mounted so that an axis over travel will not crush the switch.
- Home switches should be of the type designed for CNC use. Do not use long throw general automation / farm equipment limit switches.


Home Program: A G&M code program (aka macro) that commands the machine tool axes to move and seek the home switch trigger event, stop, back off to clear the switch and set machine home at that location.

Limit Switch:

- A switch use to indicate to CNC12 that an over travel event has occurred.
- A limit switch trigger causes a CNC12 Emergency Stop event.
- Typically used as last resort machine tool axis over travel crash protection
- Limit switches should be “Normally Closed”. “Normally Closed” = Closed when NOT tripped.
- Limit switches can be wired to individual inputs or all switches wired into one input called “LimitAll” (to save on inputs)
- Limit switches should be mounted so that an axis over travel will not crush the switch.
- Limit switches should be of the type designed for CNC use. Do not use long throw general automation / farm equipment limit switches.
- Limit switches are active all the time but can be ignored by CNC12 when commanded to.
- CNC12 can be commanded to ignore a limit switch, this is used to allow jogging if a limit has been tripped (or other special cases where it is necessary to ignore a limit for a short period of time)
- Typically mounted so the Limit switch triggers some distance before the actual end of travel of the axis and used in conjunction with a polyurethane bumper to adsorb the axis coasting to a stop after the limit event has been triggered.
- When ever possible mount switch so that the switch does not move with the machine so the cable going to the switch doesn’t get fatigued over time. When not possible pay attention to limit cable wire routing and strain relief to minimize fatigued and use good quality cable designed for movement.


Cons of using limit switches.
- Expense in the components and labor to wire
- Issues cause by durability especially in large format machine tools. Such as false limit trip message due to improper grounding, power supply issues, limit wire breakage due to fatigue in track ways etc.

Pros of installing Limit Switches
- Insurance to prevent unexpected damage to the machine tool. A good idea for machine tools that can not withstand an axis over travel event.

Limit Switch Discussion:

CNC12 Software Travel Limits works so well that it has largely eliminated the need for axis limit switches on many machine tools. Software Travel Limits work in the case where either the G code part program or the user commands the machine to move beyond its useful working envelope. It is however, up to the integrator to decide whether or not to use limit switches and how to best configure them for his particular application.
A case where the Software Travel feature will fail is when there is a catastrophic axis motor drive failure and the drive failed in the full power mode (aka axis motor runaway). In this case, a proper Limit Switch (and cnc control estop contactor wiring and a bump stop) would protect the machine tool from axis over travel crashing. Luckily at this day and age axis motor drive runaway is quite rare on modern drives. But, for the best machine tool damage protection use Limit Switches on all axes on both plus and minus ends of the axes and use an Estop contactor so the Axis motor drive power is disconnected from the axis motor automatically when a limit switch is tripped.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cnckeith
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Re: Home all and limit all

Post by cnckeith »

Wizard Home Input Name
Description


HomeAll
One input for all Home Switches.
FirstAxishomeOk
Used for individual inputs for each home switch. One input for Axis #1 home switch
SecondAxishomeOk
Used for individual inputs for each home switch. One input for Axis #2 home switch
ThirdAxishomeOk
Used for individual inputs for each home switch. One input for Axis #3 home switch
FourthAxishomeOk
Used for individual inputs for each home switch. One input for Axis #4 home switch
SlavedHomeInput
Used with the Centroid supplied canned autosquaring paired axis routine. See Paired Axis installation manual.
ZriHomingAll
Input for axis motor encoder index pulse (aka marker pulse) homing






Wizard Limit Input Name
Description
LimitAll
One input for all Limit Switches.
FirstAxisMinusLimitOk
Used for individual inputs for each limit switch. One input for Axis #1 minus direction limit switch
FirstAxisPlusLimitOk
Used for individual inputs for each limit switch. One input for Axis #1 plus direction limit switch
SecondAxisMinusLimitOk
Used for individual inputs for each limit switch. One input for Axis #2 minus direction limit switch
SecondAxisPlusLimitOk
Used for individual inputs for each limit switch. One input for Axis #2 plus direction limit switch
ThirdAxisMinusLimitOk
Used for individual inputs for each limit switch. One input for Axis #3 minus direction limit switch
ThirdAxisPlusLimitOk
Used for individual inputs for each limit switch. One input for Axis #3 plus direction limit switch
FourthAxisMinusLimitOk
Used for individual inputs for each limit switch. One input for Axis #4 minus direction limit switch
FourthAxisPlusLimitOk
Used for individual inputs for each limit switch. One input for Axis #4 plus direction limit switch





Wizard Home/Limit Input Name
Description
FirstAxisHomeLimitOk
One switch used as both a home switch and a limit switch for Axis #1 using one input per switch
SecondAxisHomeLimitOk
One switch used as both a home switch and a limit switch for Axis #2 using one input per switch
ThirdAxisHomeLimitOk
One switch used as both a home switch and a limit switch for Axis #3 using one input per switch
FourthAxisHomeLimitOk
One switch used as both a home switch and a limit switch for Axis #4 using one input per switch
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cnckeith
Posts: 7164
Joined: Wed Mar 03, 2010 4:23 pm
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Re: Home all and limit all

Post by cnckeith »

If you want to do something different than what the Wizard provides (which is a lot!) that is easy too. see the Acorn Macro Programming guide that has examples of custom home programs.

https://www.centroidcnc.com/centroid_di ... amming.pdf
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
TopQuarkDoc
Posts: 20
Joined: Sun Nov 29, 2020 11:12 am
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CNC Control System Serial Number: F045DA7F1D5B-0109191641
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No

Re: Home all and limit all

Post by TopQuarkDoc »

Wonderful write up for people searching for information in the future. Thanks for the time to put it all in one place.

My question was about using the same switches for home and limit trying to combined HomeAll with LimitAll. This was a try in using just two inputs on the Acorn. Using the Wizard generated cncm.hom, a bench test with the limit/home switches series and then jumpered between the HomeAll and LimitAll inputs on the Acorn causes the limit condition to be raised immediately after the first axis is homed. Looking at cncm.hom, I would have thought that the M94 /101/102/103 was suppressing the limit input sensing By setting the input port bits high. Is the "/101 /102 /103" mapping to Acorn input 1,2 and 3? The documentation clearly states that one can force CNC12 to ignore the limit condition. Is the M94 - M95 combo the right approach to deactivation/reactivation of the limit sensing function, and what is the correct input port number scheme/syntax for these commands. Trying for HomeLimitAll using two input pins. Admittedly, I could dig through the PLC code to figure this out, but hoping for a quick answer.

Thanks very much.
cnckeith
Posts: 7164
Joined: Wed Mar 03, 2010 4:23 pm
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Re: Home all and limit all

Post by cnckeith »

roger that. HomeAll and LimitAll only use one input each so that's using only 2 input 'pins' as you say. (am i misunderstanding how many inputs you want to use?)
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cncsnw
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Re: Home all and limit all

Post by cncsnw »

My comments:

If the document is supposed to be Acorn-specific, it should be titled that way.
If the document is supposed to apply to closed-loop controls as well, then it should mention that the normal M91/M92 homing sequence on closed-loop controls will back off until the encoder index pulse is found, making it quite tolerant of small variations in the switch-clear position.

On closed-loop controls, and as far as I know on Acorn controls as well, tripping a limit switch is not a Fault; does not open the E-stop contactor; does not take away the drive enable; and therefore does not require re-homing.

In the general "limit switch" section, you should note that one of the most important cases where CNC12 will "ignore" a limit trip is when the same input is designated for homing: if we are homing to a home switch on a given input, and that input is also designated as a limit switch, then the M91/M92 homing sequence is allowed to trip and clear that switch (just once) without triggering a "407 ... Limit Tripped" error.
CNC12 Software Travel Limits works so well that it has largely eliminated the need for axis limit switches on
many machine tools. Software Travel Limits work in the case where either the G code part program or the user
commands the machine to move beyond its useful working envelope.
This is true, as far as it goes. The most important case where software limits do not work to protect the machine, is on an axis that is prone to losing position. The most common position-loss scenarios as dropped command pulses and spurious command pulses on open-loop step-and-direction systems (i.e. Acorn). You do not have to look very far on the Acorn forum to see that DIY Acorn builders routinely build systems that lose position. Given that those same builders are the audience for this document, and that everyone who reads it will be convinced that noise, interference, and position loss are things that only happen to other people, it might be best to encourage them to use limit switches as the default. They are free to ignore that advice at their own risk.

Also, if the document is intended to apply to Centroid DC-drive systems (i.e. Allin1DC), then it should mention that INP1 - INP6 are hardware limits: that, if you do not have genuine normally-closed limit switches for each direction of each axis, then you must defeat the inputs for those axes and directions that lack a switch.
cncsnw
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Joined: Wed Mar 24, 2010 5:48 pm

Re: Home all and limit all

Post by cncsnw »

And a question for Keith:

As far as I know, there is no reason in CNC12 that an Acorn system could not have:
Three minus limit switches, wired in series, to one input. For this example call it INP1.
Three plus limit switches, wired in series, to another input. For this example, call it INP2.

Then, on the Machine Configuration -> Motor Parameters table:
Designate INP1 as the minus limit input for all three axes
Designate INP2 as the plus limit input for all three axes
Designate INP2 as the plus home input for all three axes

You would then set all three axes to home in the plus direction.

This should provide the same functionality as your suggested LimitAll + HomeAll scenario, using just two inputs and just six switches, but should provide the added safety that, if the machine runs past the plus limit after homing has been completed, a "407 ... Limit Tripped" error will stop the machine automatically. I think that is what the original poster in this thread was trying to achieve in the first place.

My question is: how do you accomplish that using the Acorn Wizard?
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