Machsupport Forum
Mach Discussion => Mach4 General Discussion => Topic started by: ryno3 on March 03, 2023, 03:22:01 PM
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Recently purchased a YCM supermax that had been retrofitted to Mach3. They used the original SEM brushed servos with Gecko G320 servo drives with optical encoder feedback to the Gecko drives. They connected the glass scales to a sound logics encoder interface card which feeds back to a PMDX 122 connected to a USB smooth stepper. I bought the machine not working as they had a mother board issue and couldn't recover from it and lost interest. I have the machine moving and will run some programs this weekend to test operation. I am thinking about updating it to mach 4 and updating the PC, just curious if anyone runs a similar combination and went from mach3 to mach4? I was thinking I might try to the XP version of MACH 4 to get things working and then update the PC just so I have a backup with the current version of MACH 3.
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HI,
I was thinking I might try to the XP version of MACH 4 to get things working
Why? If you are going to use Mach4 why castrate yourself with such an old build of Mach4?
Mach4 has quite a learning curve and you'll come to hate it BEFORE you get a handle on it and get to love it.
If you persevere you will get results and you never turn Mach3 on ever again.
With a capable external motion controller like an ESS then just about any PC will do....but not as old as XP!!!
One of the kids cast-off school laptops will be fine.
Can you draw a diagram of how the glass scales are connected? Neither Mach4 or Mach3 which preceded it, are feedback control solutions,
neither are the USS or the ESS. It's possible to use glass scales to monitor the machines position and even populate the DROs but that
cannot be used to close a position loop. This is why I'm interested in how the glass scales have been used.
Craig
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The glass scales are connected through the encoder interface board, and are just for display as far as I can tell, I am very new to Mach so I've been learning the past week as I worked on getting everything working again. Thanks for the recommendation on the PC, I was thinking of getting a touchscreen/all in one to put on the machine and I have several old laptops that should have enough HP to function in the mean time. I'll update more this weekend when I can look through all the settings for the encoder feedback.
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Hi,
The glass scales are connected through the encoder interface board, and are just for display as far as I can tell,
Yes, that was my guess. Well, the good news is that if you use an ESS and a good breakout board then you can hook all your glass scales
up without any interface board. Really is there any need for glass scales? I've been using Mach4 and an ESS for eight years and the only time
the DROs get 'out' relative to machine position is if the steppers have lost steps and that ONLY ever happen when I make a big mistake.
I don't have glass scales and don't need them.
Craig
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I think the builders thought process was to leave the glass scales to allow manual operation. I was having a Z axis issue trying to get it running again as it would error out and e-stop and the only thing I could find was a broken wire on the sensor for the z glass scale, once I repaired the wire I quit having issues with the Z. From what I understand Mach 4 has error logging that might have captured the cause. How buggy was the version that runs on XP and could a guy have both 3 and 4 installed on the same PC and use one or the other?
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Hi,
How buggy was the version that runs on XP and could a guy have both 3 and 4 installed on the same PC and use one or the other?
It was never that that build of Mach4 was buggy per se, in fact Mach4 has never been buggy in the same way as Mach3, but rather the old
builds miss many of the new features, like McSurface plugin, the script based THC module and so on.
Eight years ago when I started to install Mach4 my intention was to have both Mach3 and Mach4 available on the same PC. It is possible, although not eminently practical.
It took three to four weeks of extreme frustration and painful learning before I got Mach4 running satisfactorily, but once I did I've never touched Mach3 ever again.
I've lost my Mach3 license file and can't be bothered trying to get another. I seldom bother replying on the Mach3 board anymore, or at least quite selective about those threads
that I can be bothered with.
It's when you come to customize the behavior of your machine, be it modestly or majorly, that's when Mach4 shines. That is not to say that Lua, the API and Mach's
program structure do not incur a learning curve all of their own, but once you master that and you'll look back at Mach3 with pure derision.
My recommendation is embrace Mach4, and do what it takes. It will be a rough ride for a while and saddling yourself with trying to keep Mach3 limping along at the same time
is just masochism.
Craig
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Hi,
if you like that sort of thing....have I got a deal for you.....'A self-whipping stick'.....if you use on yourself it hurts like 40 bastards! I'll sell it to you cheap, I don't
need it anymore, I got rid of Mach3 years ago. ;D
Craig
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:) :) ;)
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Hi Tweakie,
the humor is a bit extreme, but I just can't help myself! ;D
Craig
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Thanks for all the feedback, completed the conversion over the weekend. Big improvement in my opinion. Still have some items to fine tune, also went with the mill wizard software which is handy.
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I think you might find that your glass scales go to the servo drive, which uses, somewhere in its logic a step and direction control. The reason I say this is, I have several boards that take step and direction from the PC and have encoder inputs, and analog outputs to the servo drive.
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Hi,
there are servo drives that can accept a glass scale input in addition to the normal rotary encoder....but they are not common and command a premium over servos that have a rotary encoder
alone. For example Delta A2 series servos:
https://www.fasttobuy.com/ecmac10807rsasda20721f-delta-220v-750w-239nm-3000rmin-80mm-dmcnet-ac-servo-motor-drive-kits-with-3m-cable_p27766.html (https://www.fasttobuy.com/ecmac10807rsasda20721f-delta-220v-750w-239nm-3000rmin-80mm-dmcnet-ac-servo-motor-drive-kits-with-3m-cable_p27766.html)
This servo will use the rotary encoder for velocity and torque loops but can close the position loop on a secondary encoder like a glass scale.
In earlier times with analogue servos it was more common to use linear scales to close the position loop, however those servos typically had a tacho generator
on the servo shaft that was feed back to the servo amplifier to stabilise the velocity and torque loops. Such servos are now rare and fading away into history.
There are motion controllers like the Hicon and CSMIO/A that can close the position loop using a linear scale, but note they produce an analog output voltage for the transconductance amp,
not Step/Dir.
There are servo drives like the Gecko G320 for instance that accept Step/Dir input, with encoder feedback, but to my knowledge must be fed with a rotary encoder, rather than a linear encoder.
Any dither associated with the difference between a tightly coupled rotary encoder and a rather more loosely coupled linear scale will absolutely screw the torque loop bandwidth, and
once that's happened all bets are off.
Craig
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Any servo drive that accepts incremental quadrature input from rotary encoders can be run from an incremental quadrature linear scale, however the scales have lower effective resolution and are not coupled as tightly mechanically to the motor. Mechanical backlash will cause problems. Typically you will have to tune them to operate more slowly with lower P gain, more I gain, and if available a dead band in order to be stable. Anilam did this on some of their older controls.
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Hi,
Typically you will have to tune them to operate more slowly with lower P gain, more I gain, and if available a dead band in order to be stable. Anilam did this on some of their older controls.
This is equivalent to reducing the bandwidth of the torque loop.
A modern AC servo has a torque loop bandwidth of about 5kHz, resulting in a velocity bandwidth of about 1kHz and a consequent position loop bandwidth of 200Hz.
The critical point is the you need the highest possible torque loop bandwidth, because that in turn results in the best possible velocity an position loop bandwidths,
with the position bandwidth being what we are interested in, where the 'rubber meets the road' so to speak.
Any backlash or non-linearity of the linear scale severely curtails the high frequency accuracy of the torque loop, say down from 5kHz to 1kHz. If I'm not mistaken those
Anilam systems had tacho-generators on the servo shaft? This was to stabilise the velocity loop and thereby retain sufficient bandwidth for the position loop.
So the torque loop would be say 1kHz, the stabilised velocity loop 500Hz for a position loop of 100Hz. A 100Hz position loop was considered pretty damned good
for many years, and would still be entirely adequate on any hobby machine today.
Today with the likes of the A2 servo you can have high bandwidth torque and velocity loops by virtue of the high lineraity and resolution of the rotary encoder BUT
also the ability to 'load sense' with a linear scale for example. Best of both worlds. All the top servo manufacturers seem to have models that have the dual sensing feature,
but they all command a premium.
I buy Delta B2's, a 750W example costs me $438USD plus shipping. a 750W A2 (basic L version) from the same supplier is $682, so a $240 premium.
I am still only scratching the surface of what the B2 offers without paying for even more that I cant use!
Craig