Machsupport Forum
Mach Discussion => Mach4 General Discussion => Topic started by: Velvetrevoultion on December 29, 2021, 05:53:55 PM
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I am considering a retrofit of an existing 3 axis CNC mill & looking for some advice about it.
At the moment I know zero about the subject of Mach4. I have very limited knowledge of CNC in general & I have to admit that the majority of my knowledge comes from trying to bring this machine back to life.
Cut a long story short I have repaired about ten things on here back to original 1991 spec, run it succesfuly without guards on for a bit & then today put the covers back as they should be & hey presto - It stopped working & put me back to square one. I am sick of this antique tomfoolery & want to bring it into the 21st century. It is way too nice to throw in the scrap in fact geometrically it is perfect & the spindle is lovely.
A mate mentioned Mach4 a while ago & it looks very good. The issues which I feel might make this too difficult & expensive are...
1/ The machine has a closed loop positioning system which I believe is one of the things which make it so accurate & I would like to keep. It uses Heidenhain LS403 scales which claim to be 1 micron precision. It has Indramat axis motors with TDM & KDS drives.
2/ It has Indramat spindle drive & motor with a 2 speed programmable gearbox. Electric actuator 24VDC which was probably designed to operate the electric windows on a Merc wagon.
3/ Z could be horizontal or vertical but manual head change.
The machine is a MAHO MH800W, new 1991
Heidenhain 234 3 axis, similar to Heidenhain 355 & Philips 432.
Manual tool change - Hydraulic drawbolt & pullstuds.
Horizontal & vertical spindles (manual)
Spindle motor 100 - 8000 rpm. 5.5W@1500rpm 100% Controlled with Indramat KDA100
Low box 20 - 607 RPM, High box 608 - 4000 RPM
X & Z axis motor 4.1A cont, 2.2Nm, 4000rpm max . Controlled with Indramat TDM
Y axis motor 18A cont, 9.2Nm, 4000RPM max. Controlled with Indramat KDS
Y is the table & all the guards which I just lifted back on. The uncounterbalanced Y combination weighs about 1.2 tons with the basic table fitted before a job or cutting load goes anywhere near it. Designed to take a tilting table with a built in NC rotary axis. that is why the Y axis is 4 times the size of the X&Z.
The rapids are 5m/min so it is not trying to crack eggs with sticks with a 5mm pitch ballscrew. I suppose it is all about accuracy.
Do I chuck away everything & buy a load of Chinese motors & drives or can I keep the Indramat setup?
Somebody tells me the Indramat motors & drives are inseperable. This where my knowledge ends.
I have been all over the web looking for clues about these lovely but totally obsolete machines & drawn blanks, now in spite of that somehow I know the damn thing inside out. I have been all over this site prior to asking for some guidance, I think the word MAHO comes up about 5 timesper decade under Mach3, similar for Heidenhain & Indramat.
Please can somebody start this off?
Thanks.
Alec.
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Hi,
1/ The machine has a closed loop positioning system which I believe is one of the things which make it so accurate & I would like to keep. It uses Heidenhain LS403 scales which claim to be 1 micron precision. It has Indramat axis motors with TDM & KDS drives.
Mach4 is an open loop CNC software solution. If you require the PC to close a position loop then Mach4 is not the right choice, you could squeeze it out with extra hardware but its
probably not worth the effort. LinuxCNC would be a better choice if the REQUIRE the PC to close the position loop.
Most modern servos loops are closed at the servo drive.
For example my 750W Delta servos have a 160,000 count/rev encoder. If I cause Mach to issue step pulses then the servo drive drives the servo to keep up. If it overshoots it will reverse the servo until
it accurate, ie position feedback. The pulses are from Mach4 are open loop, that is it tells the sevro drive to go 10mm say, and the servo drive /servo does it automatically with highly accurate position feedback.
The only time you'd ever hear from the servo drive is if for some reason, overload for example, the servo can't keep up, with any sort of luck hardly ever, I haven't had a servo overload or Following Error fault in many months.
So despite Mach4 NOT being closed loop it can an does control closed loop servos, and on my machine I have set the resolution at 1um, although it could be much greater if I wanted.
I suspect that the servos fitted to your machine are old school analogue servos, and require that the controller provide the PID control loop. Can you post some more details about the servos and drives?
My Delta 750W servos/drives/cables cost $435USD each.......so replacing your existing servos might be an option,not cheap but would be a very direct and useful retrofit. It would mean that you do not have
to program a controller to provide PID functionality, and then tune the PID loop, no mean feat. My concern is that if you elect to reuse the existing servos you could very well get into the situation that the technical
skills required to do so are beyond you.....and that would constitute a major waste of time and resources. Replacing the servos with modern AC servo/drives is still quite a challenge but much easier that trying
to resurrect the old ones.
Just to give you some context....lets say you went with Mach4Hobby:
Mach4Hobby License $200
Ethernet SmoothStepper motion controller $180
C25 breakout board $40
3 x Delta 750W B2 series servo kits (servo/drive/cables) $1305
TOTAL $1725
I'm not in any way suggesting that you'd have to go with this suite of components, it just a ballpark type guide.
A LinuxCNC alternative:
LinuxCNC free, open source
Mesa control board $200
Brain power to program it??????
TOTAL $200
Thus you can see that LinuxCNC is very much cheaper because it allows you to resue your servos, whereas the cost of the Mach4 option is dominated by replacing the servos.
Craig
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Craig,
Thanks for the reply.
I am keeping an open mind about it.
Alec
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i think 1991 was only analog control ,there several hardware producer for Mach with for analog (sure when its analog it must be close loop because also PID need make on the controller) but as my little experience its much batter replace the servo to newer
its not big money and save you alot alot hed ace
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Hi,
Vital Systems produce the Hicon Integra motion controller which can be activated to control analog servos. With activations
it costs $1200. I would not bother, but rather replace the servos with newer units, the two alternatives are cost neutral but
by replacing the servos you have avoided the possibility of one of the original servo drives from crapping out, you cant replace them.
CSMIO/A is another Mach4 ready motion controller that handles analog servos. If you were using Mach3 I'd say do it, it good quality and performance. With Mach4
not so much, its Mach4 plugin is buggy and CSLabs have gone right off the boil as far as fixing it. They have not released any fixes for over a year.
The CSMIO/A costs 600Euro. I find it hard to recommend to spend that sort of money only to get crap support from the manufacturer not matter
how good the controller is.
Craig
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If it goes this way then it because of the dreadful expense of looking after these old parts so I would try to keep it modern as possible however not keen on doing R&D on a new model of controller. Part of me says Fagor & damn the expense.
I was out there again today trying to work out why assembling a few guards has caused total despair. Turns out it is because the machine has been switched off for 2 weeks & it is cold & damp in this miserable economic area we call Britain & there is still one more day to go before they declare another year of nonsense rules & regs . So an enclosure heater is on the way.
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Hi,
as I posted earlier, yes it is possible to make Mach4 operate analog servos, but the extra hardware cost (Hicon or CSMIO/A) and that you would retain your otherwise obsolete
servos count against that course of action.
If you are dead set on retaining your existing servos then LinuxCNC/Mesa is the answer for you. You will have to accommodate the programming and tuning as best you may,
its a direct consequence of the choice to retain the old school servos.
Modern CNC control technology has moved very distinctly away from controllers that close the loop, ie PID capable, to distributed motion control. The PC or trajectory planner
issues numeric trajectory data to the various servo drives and each servo drive plans and executes it part of the overall motion. The communication protocols are numerous
but EtherCat, ProfiBus and CANOpen have come to dominate. If you were thinking about a modern controller then you'd be a fool to overlook these new control paradigms.
An open loop Step/Direction software solution like Mach4 is still a later generation than a PID capable controller, but not at the 'bleeding edge' like EtherCat. Having said that
Kingstar DO have a Mach4/EtherCat solution, and certainly worth investigating.
It all comes down to the choice as to whether to replace the servos or not. If you choose to replace then you go down one path, if you choose not to replace you go down another.
Post some pics and as many details about the existing servos and drives as you can.
If replacing the servos is on the cards you need to determine exactly what they are. I would guess that they are genuine NEMA sizes, in which case you want to restrict your search for
replacements to NEMA servos, as they would be bolt-in replacements. Delta servos are metric, and while very close to NEMA not identical so retrofitting them can be tricky
even if 'bang for your buck' favors them.
Craig
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Totally understand the playoff with old & new servos & drives. Not familiar with all these new terms but I will look them up. Effort to preserve the antiquity has been the first choice & is a bit shaky so If anything gets done it will be with new servos & new tech. The slides, bearings & ball screws are lovely. So the glass linear scales could go on Ebay & maybe pay for some of the new tackle.
The motors are German so it could be either way. I will measure later.
Now this might look as if I want someone else to read it & do all the work but actually it is the easy way to post everything I know about it. All the books & params, everything
https://drive.google.com/drive/folders/1HKzVxqxqxS7pG9r5QkctBwCr2LQ7pGUa?usp=sharing
No dims in there for the motors but the drawings show their spec.
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Hi,
The slides, bearings & ball screws are lovely. So the glass linear scales could go on Ebay & maybe pay for some of the new tackle.
The motors are German so it could be either way. I will measure later.
I think your idea to replace the servos is the best choice, as you say the rest of the machine is superb....and you really want to retain that.
You might want to reconsider throwing out the linear scales.
Amongst the features of modern servos is the concept of dual encoders. Each servo will have a rotary encoder attached to the servo shaft, per normal, and
is absolutely essential for Field-Oriented-Control servos but can accept a second encoder (or linear scale) attached to the machine, called 'load sensing'. It will accommodate
any lash or other non-linearity of the machine and is the LAST WORD in position control. This possiblity should be considered very seriously if you already have good linear scales
For instance my 750W Delta B2 series servos, with 160,000 count/rev encoder and NO load sensing, ie the entry level Delta servo is $435 (servo/drive/cables)
The 750W Delta A2 series, with a 1,280,000 count/rev encoder AND load sensing is $540. Thus you get that load sensing feature and a better encoder for about an
extra $100.
This would turn your old but mechanically superb machine into a very much more modern machine with state of the art position sensing and control. Sound appealing?
Craig
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You have exposed my lack of understanding of closed loop.
This machine has feedback from rotary encoders on the motor shaft which is backed up by linear scales =Closed loop in my understanding.
Need to learn new jargon I think.
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And that is why I am at my wits end with it at the moment. I think the drives are too cold & unresponsive. The Heidenhain control keeps going on strike because the slideway movement does not corelate to the expected movement by some miniscule amount. Thermal one way or another I reckon.
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Hi,
This machine has feedback from rotary encoders on the motor shaft which is backed up by linear scales =Closed loop in my understanding.
Note quite. All servos have a rotary encoder so that the servo drive, or PID controller, knows the servos angular position and can compare that to the commanded
angular position, and drive the servo to close the error between the two. But we don't specify angular position, we specify '6.342mm from there' or '12.687mm absolute'.
In an ideal world you could convert any linear measurement into and angular displacement of a ballscrew. This relies on the ballscrew being lineraly accurate and no
backlash. Much expense is encountered to ensure that is the case, but inevitably there will be some variance between angular position and linear position, and that variance
will be the basic accuracy of the machine.
If however you have good linear scales then you can compare linear position to angular position, with usually linear position being the more accurate, and demand that the servo
alter position to minimise the linear error.
All Feild-Oriented-Control servos, normally called AC servos, and the current state of the art in servos, require a very accurate and immediate knowledge of the angular position of the servo
in order to operate, and thus MUST have a rotary encoder. What I have elluded to is that you can have dual loop control, where the rotary encoder is used in the torque and velocity loops, but
the load sensing encoder/linear scale is used to control the position loop. As I say this is the last word in machine position control. If you can have it ....you want it!!!
This scheme would maximise the excellent mechanical properties that your machine has.
Over the course of time it is servos and particularly servo drives that have advanced and result in the machines we have today. Your machine is well built and rigid and would compare favourably
to any machine made today in terms of mechanical accuracy and rigidity. What a modern machine has is a much more sophisticated CNC control....and less, surprisingly enough, about the controller
or PC, but the smarts built into the servo drives. In this example we are talking about the servo drive, a Delta A2 series, offering this dual loop feature. The PC/controller can and is in fact fairly
basic, its the servo drive that adds the state of the art feature and the increased resolution and accuracy that comes with it.
Now I'm not saying you could not get your existing analog servos (with rotary encoder) AND the linear scales to operate in the same manner with LinuxCNC, but unless you are an experienced realtime
programmer it would not be easy, whereas using suitable AC servos then its (comparatively) easy.
Craig
Craig
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Hi,
depending on the age of your servos the situation could be different and worse than you suppose.
In the early days,and to be honest, I would think predates your machine, the servo did not have an encoder, but it had a tachogenerator, or a speed sensor, and that was
feedback to the servo amp and it assisted in the closing of the velocity loop and the controller (PID controller) took encoder, or more likely linear scale feedback and
used it to close the position loop. Then in later years the tachogenerator was replaced by a resolver, which serves a similar purpose to an encoder, but encoders were at that
time incredibly expensive and fragile.
When I went to University and studied Control Engineering, many of the systems I studied and very extensively experimented with, and was tested, TESTED, and TESTED
on were of this type. We could at that time really only dream of Field-Oriented-Control being practical.That was in the early 80's. By the 90's however encoders and microporcessors
had advanced that much that Field-Oriented-Control was feasible and by the late 90's was de-rigour in the servo industry.
Advances in microprocessors, encoders, fast power electronic devices has only ever increased since.
I can buy a microprocessor that can do floating point single-cycle -multiply-and-add at 90Mhz, with a whole suite of advanced peripherals for rotating machinery control for $20!!!!
A few years ago that was unheard of. Likewise I can buy a 1200V 20A MOSFET for $5.00 that can switch all day at 100kHz...amazing.
If you do buy new servos you are in effect buying into this evolution of electromechanical devices, and while not for free, at prices which only ten years ago would have been
considered impossible.
Craig
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I have been a bad lad & spent most of the day putting this back together.
X & Z axis motors are 4 1/2" square with 95mm square hole pattern. About 8" long including encoder cover. Don't know the shaft size. I buried the other motor before I remembered to measure. I think that makes the small axis motors NEMA45. Plate & mounting are in the attachments.
Ratio of X is 20:92 on a 6mm single start screw & backlash is approx 1/2 a pitch on the primary pulley (9 deg) which works out at 0.0175mm lost motion. So obviously some of the polish has come off the machine in 30 years.
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That is the spindle motor plate in the previous post. Here is the X axis & Z axis motor
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Hi,
OK, the top name plate, the spindle , looks to be an asynchronous (induction) motor of 5.5kW, quite a substantial motor.
It would need a 230VAC three phase input VFD. Looks like the speed range is 1500 to 8000 rpm. It would make sense to reuse this
if its in working order. Is there a VFD/driver built in for this motor?. If there is and its working then by all means retain it.
The bottom name plate is less clear.
Maybe some German readers are following this thread and can help.
Md.konst =0.44Nm motor constant 0.44Nm/A
Dauer 2.2 guessing this is rated torque 2.2Nm
Dauerstorm 5.0 translates to constant current 5.0A
nmax 4000 rated rpm 4000
This suggests a power of (4000/60)x 2PI x 2.2 =921W and is consistent with the size of the servo.
Given that the servos are not direct coupled suggests that fitting metric motor would be possible if a little fiddly.
It would require you make a new plate to take the new servo, but should be able to screw the plate to the existing threaded holes.
If I were you I would be looking for some 750W servos, or if you want a little more then 1kW servos. I think 750W would be more
than enough, and as they are a common size can be had very competitively priced.
If you don't want load sensing servos then 750W Delta B2s are perfectly fine and cheapest being Deltas entry level.
If you want load sensing, either immediately or for the future, then 750W Delta A2 series.
B2 for $438USD:
https://www.fasttobuy.com/flange-80mm-239nm-ac-motor-driver-kits-with-3m-cable-220v-075kw-cnc-servo-motor-for-cnc-router_p28084.html (https://www.fasttobuy.com/flange-80mm-239nm-ac-motor-driver-kits-with-3m-cable-220v-075kw-cnc-servo-motor-for-cnc-router_p28084.html)
A2 for $634USD:
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)
Note that I have seen advertised elsewhere these A2 servo kits for only $50 more the the B2 kits....it may pay to do a little more searching,
although I have faith in this supplier.
Note this same company has their own brand of servos, ToAuto, which are very well priced. I have no reason to doubt
their quality or performance but they wont have load sensing and they don't have set-up and tuning software.
If you are new to servos then having good (free) set-up and tuning software is to my mind essential. This forum and CNCZone is littered with posts
about people who've bought el-cheapo Chinese servos and then struggle to get them to work. Its not that they won't work, but if you've never
set up a servo from scratch before it is a challenge. I would not recommend you start your learning curve there, buy either DMM (Canadian brand, made
in China) or Delta (Taiwanese brand, made in China), both are good quality, good backup and most importantly set-up and tuning software.
Craig