Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: DennisF on September 10, 2011, 05:58:56 PM
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Hi Guy's
I have a question for you mach guru's is there a way to stop mach feeding g-code when the drives fault out i hope i am getting my point across what happens is if the drives on my machine fault out mach keeps running the code and the part and now code won't match is i do a reset and run i have to try and set the start point and run the code until i get it to a point where i can check it's location then return to 0 make an adjustment and try it again it's a real pain thanks.
Rg's
Dennis
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If your drives have a fault signal you can feed that to Mach to do an E-Stop.
The way I do it is via my PLC, heres a screenshot of the E-Stop to Mach via my PLC but you could do similar with a Brain. I also have the enables to the drives in a similar fashion in the PLC so if a limit or E-Stop button or drive faults then enables are taken away from the drives.
Hood
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Hood
Thanks for the reply, i have all my drives linked together so if one drive faults they all go didn't want any thing moving and cutting in only one axis i have break out board in between my computer and the drives so i am not sure how this effects what you have pictured above or how it's done.
Thanks again for the help
Dennis
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I take it your drives have a fault signal then? If so feed that to an input to Mach and have a brain look at that input and call an E-Stop.
Hood
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Another trick is to bring your fauilt signal into the Estop input pin.
(;-) TP
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Another trick is to bring your fauilt signal into the Estop input pin.
(;-) TP
Thats the preferred way I would say, its what I do but as I use a PLC its easy to have all sorts in the E-Stop string to Mach. I have dual E-Stop string, the one to Mach and the other to my drives contactors etc.
Hood
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Thanks guy's for the help
so then all i have to do is take one of the input line's in the Lpt port wiring and tie it into the fault wire is my thinking correct?
Dennis
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or you could also put it in as Input 1 then enable the option on General Config page (lower left) That will stop code when the input is active however it will not E-Stop Mach.
Hood
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Hood
if i do the above on pin one it would stop Mach and the G-code feed at the time the drives fault correct ? that's what i wish to accomplish when and if the drives fault out mach stops the code from going any further it all comes to a stop at the same time.
Dennis
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Yes thats what would happen, you just have to remember to rehome as you will likely have lost position but you would likely do that anyway. Personally I prefer Mach gets an e-stop but thats just my personal choice.
Hood
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Hood
what you mentioned above is what's happening, but with a twist my drives fault and mach keeps feeding the g-code i see it and stop mach then i have reset the drives and rewind the code then try and find my exact home position which is not all way's exact. What i do is run the machine until it gets to a point where i can gauge how far it's off and then home it back to zero and jog the machine i do this on both the X and Y axis this is what i am trying to get away from.
Dennis
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If you have accurate home switches then you would not have these problems. Home the machine on start up jog to where you want the offset zero to be then if for any reason you get out of position and need to restart at any point in the code its just a case of re-homing and doing a Run From Here.
This also brings up a question, it sounds like your drives are constantly faulting, why is that? there must be something wrong somewhere.
Hood
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You would still have to "accurately" reset the point of origin X0Y0(workhome) to be able to restart. Unless you programmed everthing based off of Machine Zero(refHome) OR have Fixture offsets preset to the part. SO really Refhome does not gain you much.
Irregardless IF you loose a drive(fault) you have to reset everything anyway, there is NO going back from that point.
Just a thought(;-) TP
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SO really Refhome does not gain you much.
Just a thought(;-) TP
Terry please explain why you are saying that?
Hood
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With Mach3 it sets itself up in machine coord everytime you startup. It is not required that you refhome to do work. Just clamp a pierce of material to the table. BUT then you must set the point of origin for the part to be machined. So you touch off the material and zero the table X0 Y0. You have just set G54 as your fixture offset.
You never machine in machine coords so really it does not matter where they are to mach it is just a reference base.
So lets say you crash mach and need to resetup to begin again.Simple just go back and touchoff on the material set XY to zero and off you go again.
SO unless you program your part origin based on the machine zero you still have to set the work offset to verify it is correct so WHY double your work.
Many Low End machines today do not even HAVE a homing system they run in User co0rds(work offsets) just like in Mach's case.
I have USED both types of systems and I do not see any difference in crash recovery except the Refhome method takes longer on startup and crash recovery. The machine accuracy level is exactly the same.
NOW IF you have a dedicated table full of fixturing and have setup Fixture offsets for all the fixtures THEN refhome makes sense as then you only have to set the MachineZero to establish the POO for ALL the fixtures at once. BUT you can still do that manually in mach you do NOT have to have switches or wiring to do so.
Just a thought, (;-)TP
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Terry to me there is nothing simpler than pressing RefAll to home to switches when you first start the machine, jog to where you want the X Y zero position to be and zero the DROs then off you go. Anything goes wrong and you need to restart or pick up at a point in code its just a case of RefAll again then you are all set.
Even stopping the machine half way through a large job, shutting down overnight and restarting the next day only requires a RefAll and you are all set, no pissing about with having to touch off which in itself may be a time consuming process, especially if accuracy is needed.
Just my thoughts ;)
Hood
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Hood You still have to TOUCHOFF to accurately set the X0Y0Z0 to the material or fixture or vise,etc
(;-)TP
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Only the first time Terry ;) The difference between the way I work and the way you work is the Referencing at the beginning, if nothing goes wrong or you do not have to shut down and come back another day then your way is quicker. If however you have to whack the E-Stop or need to call it a day half way through then I am sure a RefAll to the switches is a lot quicker than having to find your parts zero position again, especially if its been machined away ;)
Also makes using a fixture a breeze as you can come back day after day and never have to touch off again unless you have changed the G54 (or whichever offset you had set)
Hood
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Hood and Terry
I am currently using what Terry is saying, if the drives fault then point of origin for the part is lost in some part cases i have to put the point of origin in the center of the material so i hope this makes my point clear as to how much of a pin it is to reset the point of origin gets machined away. As to Why my drives fault out it's a funny thing if i use the machine every day there seams to be no problem but if i work on another machine for a time and not the mach machine it fault's until it gets warmed up or something to this not sure i have checked and replaced still the same condition i am using gecko servo drives the machine has 120 volt motors so i am running them at half power they were at 100 volt's and i am running them because of the gecko drives @ 50 volts don't know if that would effect this or not.
Dennis
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Well I would say your best option is to fit accurate home switches as it will solve the PITA re-finding parts zero position over and over.
Now to your faulting, dont think it will be the volts as such as Voltage = Velocity and it is current that = Torque. Sounds almost as if there is something binding but as it heats up it clears, could even be your motors are only just capable and with cold way oil its just too much but as it thins with heating they are ok.
Hood
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Hood
As I see it and correct me if I am wrong in my thinking, if the drives fault then the original point of origin is lost and if this point has been machined away then there is no way to recover to that point again with out doing what i have been doing in the past or make a fixture to locate point of origin and start over from there.
In the past when the above has occurred and i reset and tell Mach to run from there since it has no reference to point of origin mach runs the code as if it were homed at this point and does some nasty stuff to the part.
As to the drives i use the recommended oils and went through the machine very thoroughly making sure it's up to snuff before trying to operate it, i can get the drives to fault by jogging if i do a short jog input by just briefly touching the key.
Dennis
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If you have accurate Home switches and Home when you start the machine then touch off where you want the zero position to be (and zero the DROs) you will have set up a work offset. If the drives then fault all you need to do is re-home and the work offset zero will be where it was before because the original homing set that up. So in your situation all you would do after a fault is reset the drives, re-home Mach and then do a Run From Here (taking note of the prep move to make sure its correct ;) )
Not sure how much hassle it would be but if you could disconnect the connection between motor and axis and try and see if jogging faults it. If it does then its an electrical issue, possibly even a loose wire in the geckos or bob that expands as it heats and makes better contact or could be a dry solder joint somewhere.
Hood
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Just a note, running the motors at 1/2 voltage will reduce the overall torque somewhat. I would bump the voltage up to just below the Gecko max leave a small bit for safety reasons. Volt x amps = watts = HP usually the more the better(;-)
Also Hood is correct it sounds like sticktion I would change the way oil to a less viscous oil.
On the Point of Origin WorkZero When I set up the material for the part and have established 0,0 I woul d move over to a known point on the table that is NOT going to be machined and record the position of that known point. It can be a square edge a hole or a simple centerpunch mark , just something you can rereference back to. Write it down.
Say it was X-2.000 Y-1.000
If you have to restart simply move back to the known postion and reset the axis dros to that location X-2.000 Y-1.000. NOW 0,0 will be exactly where it was before you started machining.
I normally use a Probe to probe a circle BUT any method of accurately finding the ref point will do fine.
In my opinion low end switches are NOT accurate enough to do accurate refhome repeatably.
NOW for the record I am ALL for doing it by the book BUT not to a fault(;-).
Just a thought, (;-) TP
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Terry, Optos are cheap and very accurate, only problem is keeping them dust free or dry (depending on machine type) Making a housing for them that is enclosed is not too difficult and having a rod sprung at both sides to centralise it then a flag on that rod makes a nice water/dust proof setup which is very accurate, also makes a nice project for a person to do especially if new to CNC :)
Industrial Hobbies, I think, used to sell them but dont think they do any more, when the ones I got from them eventually packed up I just made more as it was easy enough and I used the optos I always use, OPB 916B or 917B
Now I do homing in the servo drives I use as they home to a switch and then seek the index pulse.
Hood
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Thanks guys i appreciate your input.
But correct me if i am wrong when the drives fault out reference to point of origin is lost right, i can't get it to go back to where i first zeroed it.
I don't see how referencing the machine to a hole in a fixture would get it back to a point of origin on the material unless it's machined from there but then this would move the part being machined in the material i don't see this working so huh!
Dennis
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When you home to switches you are setting the machine coordinates and Mach keeps track of them. If you move to your work and touch off and zero the DROs you have set up a work offset (default G54) so if at any time you fault and are out of position you rehome and then you can go yo X Y Z zero and it will be exactly the same place as it was when you set before as Mach knows the position relative to machine coords. Terrys way will also do it but it means you are basically not homing but touching off the work and setting the offset zero then moving away to a point and touching off that and taking a note of the DROs so if you fault you again touch off that point and then set the DROs to the values you noted for that position.
So basically both do the same but to me homing is easier, nothing to note down, no second touch off, no having to touch off again after loss of position. Homing to switches is all thats needed and its automatic.
Hood
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Hood
Again many thanks to you and the others that make this a great forum for help and information. my machine has limit switches but thats not the same as a home switch wouldn't they be movable in your method otherwise terry's method would work probably with the least amount of playing with a working machine.
On the subject of the drives faulting out, if i slow the machine way down with V and accel set at 250 then i don't have the drives faulting but man it's slow moving fault seams to only happen when i kick it up to over 1250.
Dennis
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See how accurate your limit switches are by enabling them as Home switches also and doing some homing (RefAll) then jogging off a bit and touch off something and zero the DROs. Then do a Ref All again and then again jog and touch off the same part and see if the DROs read zero or very close and repeat a few times.
Sounds like the servos are just not quite powerful enough for your machine.
Hood
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In fact another way to test, assuming you are not losing any steps at the time is to RefAll, jog off a bit and do the Verify button and see what the message says it is out by.
Hood
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Another method ... Ref the machine then go to Home/Limits and uncheck Auto Zero for the axis (s) you'd like to check.
Hit ref button repeatedly and the dro will show the variations in the switches.
Might surprise you.
My first switches were off .003", next ones were .0002 - .0004"
Russ
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Hood
The servo motor's came with the machine they are very heavy duty @ 500 in Oz's of torque.with out the home switches when i use ref all and then jog off the machine it comes right back exactly to the spot it started from so no problem there. funny thing about the switches i have tried to trace them through the harness but can't seam to find them don't know whats up there i will look further into it and hopefully get it fixed.
So I guess its back to the method i was using i am just going to have to make up a fixture or device i can use when setting the point of origin.
Dennis
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Russ
Thanks for the input that's a lot when trying to hold some tolerance on a part i am now more then ever thinking my way although a pain is the best way.
Dennis
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Dennis, do you have the limits set up in Ports and Pins as Limits? If you do then no need to trace wires or anything, just enable the Home for each axis and set to the same port and pin as the limit for that axis.
What type of machine is this?
Hood
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Hood
The machine is a Lagunamatic it's a 1990 and in very good condition, not sure i understand what your saying regarding the limit switches.
Dennis
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What I am meaning, are the limit switches that are currently on your machine set up as limits in Ports and Pins in Mach? If they are then you can also enable them as Home switches so that you can Home to them.
Hood
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Hood
No the none of the switches are connected to the lpt port.
Dennis
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Ok then you cant use them, unless that is they have dual contacts (Normally open and Normally closed) then you could run the unused ones to Mach, failing that getting some optos and using them may be a good choice, not a hard thing to do and very accurate if you can keep them away from coolant. I think however your machine must originally had home switches so unless they have been removed by the person who did the retro it may just be a case of wiring them to Mach.
Or of course you could do it Terrys way and locate some feature and take note of its coords then if you loose position touch off it again and enter the values direct to the DRO.
Hood
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Hood
I did the retro myself so the wires are in the harness as i previously mentioned i guess I'll have to make choice about how or what i am going to do if i loose the drives.
Dennis