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Author Topic: CV bad behaviour need improvement  (Read 15997 times)

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Re: CV bad behaviour need improvement
« Reply #20 on: April 04, 2012, 12:28:35 PM »

so go use EMc then. or slow the feed down. use your machine within its limits.while i do not use a spindle, i cut with plasma at 6 meters per minute with no problems.

Offline nik

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Re: CV bad behaviour need improvement
« Reply #21 on: April 04, 2012, 05:28:16 PM »
the reason for all headaches was to increase the feed, not to slow it down
my machine limits are 15m/min with acceleration time 0.2 sec
I guess that the problem on my PC become noticalbe a bit early bacause of different settings, more steps per unit, or something else, but soon or later that will become a problem when you wish to improve, it looks like the problem is with the motion algorithm when tryinh to calculate CV movements
unfortunately mach3 work smooth up to 3m/min, with increasing the feed is not so smooth anymore, in some situations do not decelerate, which is unacceptable, actually 3m/min is really good speed for all DIY, even too much for steppers
emc is a bit complicated to setup all features, but I used it for 4-5 days cutting and it looks like the movements are much better, same G code with the only change - feedrate. it is moving smooth up to 15m/min on straight lines only slowing down to 6-7m/min on short-lines-arcs, but still moving so smooth, with the current tool and spindle I can cut with maximum feed of 8.5m/min, and now I can use the full potential, for now I will stick with emc on my mill
so the problem with the mill is solved and Im very happy now, same G code is executed in a quater time than before, and same quality as mach3 on 3m/min
today I tried to run a lathe with mach3 turn, currently I struggle with M6, is not changing the tools, probably I have to read a bit more
« Last Edit: April 04, 2012, 05:47:46 PM by nik »

Offline BR549

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Re: CV bad behaviour need improvement
« Reply #22 on: April 04, 2012, 06:32:43 PM »
Sounds to me yo have found the max speed that your machine can run smoothly.

IF MAch3 were NOT deaccelerating you more than likely would have tripped the servos due to servo error.

SO IF the servos can keep up then you are at the rigidity limit of the machine.  I would suggest you retune the servos for the conditions. The servos tune seperately from MACH3. You should be able to soften the servo tuning to help.

In the real world you tune the servos to the MACHINE capabilities.

(;-) TP

Offline nik

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Re: CV bad behaviour need improvement
« Reply #23 on: April 04, 2012, 10:55:13 PM »
yes, when the feed is over 6 m/min a suddent stop in step pulses trip a servo error

I tuned the servos when I build the machine and when I wrote the controller software, so Im sure they are tuned properly, I know the machine capabilities from the day I designed it, I just never was able to use it with the full potential before
the PID is tuned to keep minimum folowing error, so when mach3 stops suddently, they try to stop suddently as well, that shakes the whole machine too much, therefore mach3 shuould never stop suddently, it should ALWAYS use ramps

allowing more folowing error is not the solution, the machine run smooth as the step pulses are smooth, if the step pulses are NOT smooth, then the problem is where they are generated, you can try to calculate the overshoot whrere the speed is 6m/min and the deceleration of 0.2 sec is missing, It will be about 8mm if the servo controller decelerate, insted of mach3, this is completely unacceptable for CNC machine,
I think it will be easy for you to understand if the motors are STEPPERS then there is nothing to tune, they will just loose steps if you dont send proper step pulses

therefore I decided to locate and solve the problem instead of looking for a way to work with it, the main job of the motion software is to generate pulses WITH ramps

reading your message again make me think for the difference between good product and bad product (machine/software), good product is working as it should be, and bad product is when you try to make it work with all unsolved problems in it, if you want to make a good product, then you should solve the problems, instead of trying to go round
« Last Edit: April 04, 2012, 11:09:45 PM by nik »

Offline nik

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Re: CV bad behaviour need improvement
« Reply #24 on: April 04, 2012, 11:22:05 PM »
therefore I tried to report the problem and suggested an improvement, but as GER21 explained early - mach3 will not be fixed, we have to wait for mach4, but I will try it when is available for download and when I can use it with my current license, until then I will stick to emc even if I dont like linux and linux dont like me

Offline Hood

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Re: CV bad behaviour need improvement
« Reply #25 on: April 05, 2012, 04:04:34 AM »
TXXYY where XX is the tool number and YY is the offset number, example T0101 or T2525.
Hood

Offline nik

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Re: CV bad behaviour need improvement
« Reply #26 on: April 05, 2012, 04:17:14 AM »
yeah I found it few hours ago, last time I used tool changing on lathe was 15 years ago, completely forgot that it should be 4 digits
but thanks

Offline Hood

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Re: CV bad behaviour need improvement
« Reply #27 on: April 05, 2012, 04:56:19 AM »
BTW no need to also use the M6, you can if you wish but Mach doesnt care either way in Turn.
Hood

Offline BR549

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Re: CV bad behaviour need improvement
« Reply #28 on: April 05, 2012, 11:14:09 AM »
So you are saying that at a certain point MACH3 just STOPS following the axis tuning as far as Vel /Accel ??? I don't think so(;-) IF it did you could not make a part as the axis would be lost in 2d space.

You can MAKE the servo tuning TOO tight and get what you are describing. You can also tune Mach3 with too much accel for the velocity and get what you are describing.

Mach3 uses a bang bang planner (trapazoidal ramps)  Get the Accelleration too high and it is like running into a wall to stop. (;-)

It is still ramping but the ramp form is almost vertical which can easliy SHAKE the machine. CV can ONLY do so much to correct it. Most times it is as simple as rewriting the Gcode Micro segmented code is bad for smooth operation and the faster you go the longer the bad segments can be.

Been there done that , (;-) TP





Offline nik

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Re: CV bad behaviour need improvement
« Reply #29 on: April 05, 2012, 12:53:30 PM »
instead of guessing better read more carefully what I explained MANY MANY times
as I mentioned ALREADY mach3 was set up to 15m/min with acceleration 0.4 sec. which is smooth most of the time and still doing sudden stops at certain point
therefore must be fixed, if you set up a ramp with 0.4 sec accel and 0.4 deceleration it should use that ramp for EVERY EVERY EVERY move, no mater jogging, CV or exact stop, if you dont believe me that it stops suddenly at certain points, Im not here to make you believe, Im here to report it, if somebody care and want to fix it, it is useful information which is hard to notice, but it is ESSENTIAL for proper and fast movements

also I mentioned already that it stops suddenly when you are jogging on 100% near to software limits, the servo controllers can handle it, it is shaking but not loosing position, last night I tested  jogging near software limits on stepper motors, it is horrible, it is loosing position instantly, so I switched off the software limits
« Last Edit: April 05, 2012, 01:02:26 PM by nik »