Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: DennisF on September 06, 2010, 04:11:52 PM
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Hi Guy's
Trying to get some more speed in the X&Y travel I am using servo motor's and gecko drives i have tried upping the kernel speed to 4500 but when the machine dose a rapid it faults out the drives is the speed and the computer CPU speed connected do need a faster computer to get more speed out of the machine or is there something else i am over looking.
Thanks
Dennis
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Do the Geckos give you an error for fault finding. Sounds to me like you are getting a following error due to the increased speed and the drives not being able to keep within the following error range. Other thing could be overcurrent as the motor is drawing too much trying to accelerate to the speed.
Try dropping the acceleration and see if that helps, also maybe a bit of tuning is required, not sure how easy or difficult that is with Geckos.
Hood
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Hi Hood
Thanks for the quick reply, the machine operates very well and no problem with the processing of G-code but i want the machine to go faster if i increase the kernel speed in Mach the machine moves faster but then when it calls for a rapid move the machine studder's and the drives fault out.
Dennis
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What does the Pulse Frequency on Diagnostics page read and does it jump about a lot or is it steady?
Hood
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hood
It's very steady around 3500.
Dennis
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Too low if you have the Kernel set to 45K, it should be around about the 45K. You did restart Mach after the kernel change I presume?
Hood
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Hood
I had to change the kernel speed back to a lower speed of 3500 because of what i said above it would fault out the drives at the higher 4500 kernel speed so i set it to the lower 35 and no problem the machine runs fine just slow i have mach over driven to 300 % it's still moving slowly i timed it the machine travel is about 85 MM in 20 seconds i don't know but it seams slow to me.
Dennis
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What steps per unit do you have?
What do you mean by over driven 300%
Hood
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Hood
The machine is at 790 steps per unit and what i mean is on the mach screen there is a setting to increase the feed rate i have it at 300 right now.
Dennis
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Ah Ok FRO will only increase the feedrate (G1/G2 etc) G0 moves will always be the max set in motor tuning and also feed moves will never exceed that as well even if FRO is up to 300%.
The max rapids you will get with that kernel and that steps per unit are 2658 mm/min or 44 mm/sec
So your 80mm in 20 secs is very slow indeed. How are you commanding the move? If you G0X100 it should move at the velocity you have set in motor tuning.
Hood
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Hood
OK i see now so if the G-code calls it out at say feed rate of 80mm then no matter what i do in the FRO the machine well only move at the feed rate set in the g-code is this correct, if this is so then if i change the feed rate in the g-code to say i don't know 300 and then i find this to fast how can i slow it down do i have to stop the machine and edit the g-code to a lower speed i thought that's what the FRO was for ?
Dennis
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No, what I meant is the feedrate will never go above the rapid speed, so if your motor tuning has a velocity of 2000mm/min you can never exceed that. If you call a G0 move it wil always be at rapid speed. If you call a G1 it will be at the F you have called. Setting the FRO will increase the feedrate so if you have a G1X100F80 and the FRO is at 300% your feed will be 240.
Hope you understand, I am not making a good job of explaining it LOL
Hood
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Ok I will try again :D
If for example your rapid speed (Velocity in motor tuning) was 2000 then,
If you have F40 and 300% FRO you will go 240
If you had a F1000 and FRO 300% the max you would get would be 2000 as that is what your rapid speed is and Mach will not exceed that.
Hood
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Hood
So if i understand correctly if i increase the velocity this will move the axis faster in the code it has both G00 and G01 i am using a cam package to generate the code file.
Dennis
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Increasing the Velocity will set your Rapid speed which is the G0, what is your velocity at the moment/
Hood
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Hood
It's 750
Dennis
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Ok so F40 at 300% should not be a problem, you should move at 240 with that.
If you command a G0 move from MDI it should move at 750mm/min, does it?
Hood
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Hood
I am a running a program right now and this is what has led me to the fact that the machine is running so dam slow it's taking forever to cut the file is there a way to increase the speed right now or stop the machine and make a setting change or something.
Dennis
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Ah ok, now you have me thinking and thats dangerous ;D
Is this file made up of lots of short moves? Are you in G61 (Exact Stop mode)? if yes to these then it could well be that your acceleration is slow so the commanded feedrate is never being reached.
Hood
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Hood
OK the start code or first line of code in the file reads as follows G00 G49 G40.1 G17 G80 G50 G90 G21 don't see a G61 and yes they are all short moves
Dennis
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Do you see the green LED surrounding the CV Mode?
Hood
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Heres where I mean.
Hood
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Hood
No that is not green it's black like the dwell led
Dennis
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That is likely your problem.
When in exact Stop mode the axis has to accelerate and then slow to a stop for each line of code. If the moves are long then its not an issue but if they are short moves you would need very fast acceleration to get up to the commanded feedrate for each line.
Setting to CV (G64) will lilkely help a lot, setting a higher acceleration (if possible) in motor tuning may also help.
At the Velocity you have(750) in motor tuning 25KHz kernel will be more than enough.
Hood
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Hood
So i am not sure what i need to do should i increase the velocity and the acceleration both and change a mach setting or ?
Dennis
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What I would do for a start is use CV mode. To do that either MDI G64 or best is to have G64 at the start of your code. Also change to CV mode ( G64 )on General Config page so that Mach starts default as CV mode.
Hood
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Hood
OK i will do just that also i just found something i stop the file and then clicked on the feed rate line typed in 600 it took it and now the machine is moving like i thought it should all along funny how you find thing's like that huh i got it going now thanks for all your help you and others are what makes this a great site.
Dennis
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If you still get issues shout back and I am sure we can get things running sweet :)
Hood
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Hood
I got the machine through at least the test file so i could see what the code is doing and now i want to get a part actually cut in metal i was using a rigid foam for a test.
So first question how high can i go with the velocity setting i have Mach set at 3500 kernel speed i upped the velocity to 950 because i was not sure of how high to take it the other thing i need is to find a realistic speed and feed chart all your help is greatly appreciated oh and the machine works great it's the speed of maching a part that's the issue.
Dennis
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Hood
One more thing i would like to say is i am running an earlier version of Mach i am afraid of updating it to the latest version as when i have done this in the past it screws up and i have a hell of a time go back to a version that worked so should i wait until Brian has the version 4 done ?
Dennis
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With servos your motors rated speed determines your max velocity, or rather it should. There are several things which could affect this such as you running a lower voltage than the rated speed is given at. The pulse rate needed at that speed could be too high for the kernel.
What is the rated speed of your servos and is there any gearing between motor and ballscrew and what pitch is the ballscrew?
As for the version upgrade, what problems do you get?
Hood
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Hood
I have a Lagunmatic the servo motor are 500 in oz torque, 2500 rpm, V/K =40 V@120 DC i have them running on @ 50 Volts DC they have the normal pulley belt drive i had all the ratio's figured out but can't find it at the moment.
On the update version's i found that the graphics were bad and the arc's went wonky the present version i am using work's this is the reason i am afraid to change it.
Dennis
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So you are looking at about 1000rpm max motor speed at 50V if I read that correctly. So you can work out what the max velocity will be from there. For example if one rev of your motor moves the axis 5mm then max velocity would be 5,000mm/min, so all you need to do is work out the gearing and the ballscrew pitch and you will know roughly what your max velocity will be.
Hood
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Hood
Will this effect the actual movement in terms of part dimension's so hopefully i can explain what i mean using the midi line i do a move to check that the machine moves the correct amount say 25 MM and it dose will changing the velocity change this as i understand it that's in the unit's per correct me if i am wrong.
Dennis
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Changing the velocity wont affect the dimensions, that is as you suspect set by steps per unit so as long as you keep the same steps per you will be fine..
Hood
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Hood
OK with that said then my thinking is now that i am way down on velocity @ 950 i should be able to increase it up to lets say 4K what do you think to high or should i go a little at a time and see what the machine will take what should i expect ?
Dennis
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Without knowing the gearing and ballscrew pitch I dont know what your velocity will be.
If its a fairly large mill then 4m/min should be fine, I run my Beaver NC5 at 8M/min.
Hood
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Hood
is that M for million or ? yes it is a large mill with some big power i don't need it to go at light speed i just need it to cut at a reasonable speed.
Thanks again for your help and response to my question's.
Dennis
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That M should have been m and is for meters.
Hood
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Hood
OK you have to remember here in the US we are in a combo mode meaning metric and standard, i pump up the velocity to 3000 and then tried a rapid move through the jog control but the drives faulted out so i moved it down to 2000 seams to be OK with this amount i am cutting air right now with a file i have been working on and it seams happy also have Mach set in CV mode looks a lot better anything else you could recommend thanks again.
Dennis
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You are using metric though, aren't you?
Getting the acceleration as high as you can without faulting will make a big difference, that is where servos really score over steppers.
Hood
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Hood
Yes i am in metric G21 should i make a change to the acceleration as well i have only made the change to the velocity.
Dennis
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Try upping the accel and get it as high as you can. What kind of servos and drives do you have?
Hood
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Hood
The machine has big mho servo drives and i am using gecko 320 drives on all axis 500 line hp encoders.
Dennis
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Hood
one more thing i am really excited in 1hr 20 min the machine has now gone through over 3600 lines of code until i made the present changes it took the machine more then a day's time to process the same amount wow what a change thanks again.
Dennis
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Glad to hear its working better for you :)
Hood
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Hood
I know the machine's drives are way under power for the servos as the original ones were 100 V at the time i was retrofitting the machine these are what the budget could handle.
One thing i did notice is when changing the kernel speed from 3500 to 2500 it seamed that the machine travel was faster so fast that the drives would fault out and a mach statement came up saying the speeds that were set for the drives was to fast what is the relation of kernel speed to drive speed or how dose this work?
Dennis
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The reason you would have seen that was you had previously set the velocity higher with the higher kernel then when you dropped the kernel the velocity was above what that kernel could deliver.
The way it works is this
25KHz kernel means that you can pulse at a max of 25,000 times per second, if your steps per unit are say 1,000 then that means your velocity can be 25,000/1,000 = 25 units. BUT that is per second so you would multiply by 60 as the Velocity you enter is per minute, so that would be a max velocity (at the steps per unit of this example) of 1500 units per minute.
Using the same Steps per unit but 35KHz kernel it would be 35,000/1000 x 60 = 2100 units per minute
For 45KHz its 45,000/1000 x 60 = 2,700 units per minute
Etc etc
Hood
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Hood
Thanks that explains it very well and i will apply this to the machine sure dose run a lot better now thanks again.
Dennis
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No probs Dennis, glad its running well :)
Hood
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Hood
Thanks