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True but my intention of using one is not to protect the tool itself, but to protect the machine from crashing into the BF12 floating bearing for any unintended reason. On my current machine I've been completely fine without any limit switches, but that machine is made with weaker stepper motors and is only running 4000mm/min at maximum feed rate.Quote:
Originally Posted by Clive S
Have you considered soft limits?Quote:
Originally Posted by NordicCnc
No I have not, but that should work perfectly with position feedback from the servos. Thanks for the tip!Quote:
Originally Posted by Clive S
JAZZ, what motors are you using to drive the ball screws and is the Z-axis motor with a brake? The Z-axis for my machine will be quite the same weight.Quote:
Originally Posted by JAZZCNC
If you read one of my last posts in the build log http://www.mycncuk.com/threads/13448...823#post114823, I wrote that I will probably use Delta 400W servo motors and with a brake on the Z-axis. Well now I've got an offer for a full return from the supplier of those JMC 180W with integrated drivers, if I swap them for JMC 400W servo motors with integrated drivers. The problem here is that those JMC 400W servo motors does not come with a brake option.
A 400W servo (rated at 1.2Nm @ 3000rpm) is plenty enough. 200W is also probably enough.
I will be using a Yaskawa 400W servo with brake for a 60kg Z axis (moving part only), driven by a 5mm pitch ballscrew @ 1g accel and 20m/min.
The servo has a peak torque of 4Nm, and moving this axis will only require about 2Nm peak.
In post #2 http://www.mycncuk.com/threads/13448...672#post114672 you said that these 180W servos that I had bought were only toys and that 400W would be the bare minimum. I think you were talking about a little bit different design in that case so I can just ignore it, correct? Anyway the price difference between a Delta 200W servo and a Delta 400W servo is minimal.Quote:
Originally Posted by jarjar
Will you be using direct drive for that Z-axis? I checked that those servos are rated at 3000rpm, so direct drive with 5mm pitch would result in 15m/min. Also what diameter will that ball screw be and is it possible to spin it that fast?
Your moving weight sounds extremely heavy! Are you designing it in steel? How did you calculate how much Nm will be needed to move the axis?
Wow, this turned into a lot of questions, lol!
A JMC 180W might be enough power wise, but industrial servos are much more sophisticated. Encoder resolution, motion smoothing (much needed for high accel when the controller doesn't handle S-curve motion profiles), vibration suppression, ...
To be honest I also had a different machine in mind from what you're planning when you stated your requirements :)
For calculating the required motor, I simply plugged the numbers in Yaskawa's calculator (SigmaSelect).
It's a 2005 ballscrew coupled with 1:1 pulleys (I would have liked to go direct-drive, but didn't have enough space to inline the motor). The axis can reach 30m/min because servo max speed is 6000 rpm. Ballscrew critical speed is not a concern since it's short (400mm) and could in theory handle 13'000rpms.
Yes the axis is all steel, but the spindle is only 2.2kW ISO20 30krpm. The goal is high-speed aluminium milling.
Nordic be careful here because it's like comparing apples with oranges when comparing Yaskawa motors with Cheaper Chinese motors. The price difference is big and so is the quality. I'd also guess to get those speeds the Yaskawa will use an absolute encoder system with high count encoders requiring a high-frequency controller.Quote:
Originally Posted by jarjar
When you move up into these levels then everything else attached to them needs to move up in quality with it, else no point fitting expensive high-quality servos.
Your 8K budget will soon get eaten up with motors and ball-screws.
Delta is Taiwanese and they make proper cheap servos. Also 400W Yaskawa servos can be found rather cheap (~$400 motor + drive + cables). Most similar sized servos have the same ratings. 6000 rpm is nothing special, same for absolute encoders.
I asked a quote for the latest ASD-A3 drives from Delta with a 750W servo, 24-bit incremental/absolute encoder. Price was $350.
But Jazz is right to warn you. Servos are more complex than steppers. I went Yaskawa just because their manual is more comprehensive than the Delta one.
Thanks for the heads up JAZZ. I am set on using chinese servos anyway because of the price and their good reputation.Quote:
Originally Posted by JAZZCNC
Regarding the controller pulse output then I don't think I need to worry. The ESS SmoothStepper can output up to 4MHz according to its specs.
Would you also have time to check my questions in post #44? I would really appreciate it man! http://www.mycncuk.com/showthread.php?p=114834
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Thanks for the link to the calculation software, this will be very useful to me.Quote:
Originally Posted by jarjar
Myself I think I am going to consider a 2005 ballscrew for the Z-axis. My ball screw length is also 400mm long and who would not appreciate a 15m/min rapid feed rate! Originally I planned for a 1605 with a 2:1 reduction, since I worried about whip (ball screw critical speed) and increased inertia (180W servos). These things are no longer an issue!
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I wasn't referring to Delta when I said Chinese servo's it was a general point between Cheap and Expensive Servo's. Regards the Yaskawa motors -drive-cable package then can you post a link to where your buying because that's a very good price. What model is that.?Quote:
Originally Posted by jarjar
Regards the speed I don't see many that are rated at 6k rpm in the lower price ranges, 3K rpm is a typical rating with incremental encoders. Yes, they can be run up to 5-6K rpm but they are not rated to run at that speed constant.!
There are currently tons of offers on Ebay for SGM7J-04AF + SGD7S-2R8A00 at $450 new. I bought one like this a while back for a little less. I just asked for cables and they included them with no extra charges.Quote:
Originally Posted by JAZZCNC
You can even buy the model with absolute encoder separately for less :rolleyes: (SGM7J-04A7 $160 + SGD7S-2R8A00 $260)
I didn't say 6000rpm is the nominal rating, but it's still useful for short rapid moves.
The motors are 8Nm Lichuan closed loop steppers using 230Vac mains drives. It doesn't use a break because the gantry is vertical so Z-axis isn't fighting gravity, plus 8Nm is more than enough for this Z-axis even with heavy ATC spindle on it.Quote:
Originally Posted by NordicCnc
Regards the JMC then I've no experience using these motors or drives so I can't comment on how good or bad they are and I haven't looked at the specs, but if I'm honest I wouldn't use motors with integrated drives on a CNC machine. The heat and vibrations from the motors along with cutting debris, esp from aluminum coolant, etc, can't help with life expectancy but for me what's worse is the fact your running long signal wires back to the controller leaving you wide open to issues with interference from noise.
I totally missed that.. It is of course the X-axis in your case that could perhaps need a brake, but seems like its fine without.Quote:
Originally Posted by JAZZCNC
Would there be any chance that a 400W Delta servo with brake couldn't handle my Z-axis of around 25-30kg, with a 2:1 reduction or even 1:1? I could go for 600W if that would be better.
Got it, thanks again. I will now completely forget about these servos with integrated drives.Quote:
Originally Posted by JAZZCNC
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I believe I already answered that in details...Quote:
Originally Posted by NordicCnc
Gah you are right! In post #44 you did answer..Quote:
Originally Posted by jarjar
JAZZ, please ignore my repetitive question, and thanks jarjar for pointing out!
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I'm surprised how much these have dropped in price, last time I looked, which must admit is quite some time ago, Yaskawa kits were like $900-$1100 range for 400W. I've never used them for this reason so I may look at these when a suitable job comes up.! . . . How easy or hard are they to setup/tune.? Do Yaskawa supply the Sigma tuning software for free.?Quote:
Originally Posted by jarjar
I'm surprised the absolute encoders are cheaper as well, not as many controllers about that can accept Absolute positioning so I would have expected them to be more. Thou absolute systems and Bus/Ethercat drives/controllers are coming down in price and more popular so maybe this is the reason.?
Nordic: Forgot to say in the previous post when mentioned about higher-level servos requiring higher quality components. That this is also true to lower degree for cheaper servos over a Stepper system.
For instance, with motor coupling used on Stepper, you can get away with more springy coupler and it won't affect the motor in any way. Whereas a springy coupler on even a cheap servo system can cause big issues with tuning the motor. The same goes if using belts and pulleys, buy good quality belts and pulleys.
The stiffer you can make the coupling between motor and screws the better this goes right down to motor mounting. Flimsy motor mounts etc will cause resonance which you'll have to tune out of the system. This isn't always so easy with cheap servo's so the more you can do to limit resonance the better.
I have never used servos before so I am not familiar with how the tuning works. All I know is that the Delta servos and most of the other servos comes with some auto tuning software. How good auto tuning works I have no idea.Quote:
Originally Posted by JAZZCNC
Seems like tuning manually is very difficult and requires a lot of experience to get it right. If you don't know how to do it, the servo system would end up being even worse than a stepper system. I am starting to wonder if I would be better of with a good stepper system instead of diving into the realm of servos.
To me it seems like you favor steppers at for your own builds, but I may have got this wrong. If I am right, I guess you favor steppers for the simplicity and the above reasons?
By the way what would be a good supplier for belts and pulleys? What supplier are you using?
Thanks again for your great insight!
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Yes of course software is free. I'm not yet to the point of tuning but having read the manual multiple times I don't expect many issues. You start with the auto-tuning and fine-tune from there.Quote:
Originally Posted by JAZZCNC
IMO rotary absolute encoders are not worth the hassle. Their only use in a router/mill context is to spare you the homing after power-up. And obviously the controller must be able to interpret the special Yaskawa protocol and I think no hobby controller can at this point. It could be done with some knowledge with LinuxCNC+Mesa.
No, it's not obvious really, it's not uncommon for high-end Servo manufacturers to charge for specialist tuning software if not using their own controllers just like it's not uncommon for PLC providers to charge for programming software.Quote:
Originally Posted by jarjar
I'd be interested in hearing how you get on with tuning. What controller and which method of control +/-10v or Step/Dir .?Quote:
Originally Posted by jarjar
What hassle.? Far less wiring and setting up far as I can tell, esp if using Bus type.! . . . I've not used any yet but soon will be doing so I'll let you know.Quote:
Originally Posted by jarjar
Yes exactly for that reason! The machines I build mostly go to MEN in SHEDS type users or small business where the speed or high resolutions etc servos offer isn't needed. Reliability and simplicity are more desirable than speed for these users. Also from my point of view it also means less work and happy customers.Quote:
Originally Posted by NordicCnc
A good properly sized and tuned closed loop system is more than good enough for most builds and far simpler.
I use a local supplier.Quote:
Originally Posted by NordicCnc
Step/Dir is the most reliable and flexible. With analog +10V you're forced to control the servo in velocity mode.Quote:
Originally Posted by JAZZCNC
With Step/Dir you can control it in position or velocity mode.
I'm also convinced position mode (letting the drive close all the loops internally) is the best way since the drive can do it much faster than the controller.
The interface of the servo drive is a whole other topic and has nothing to do with absolute encoders. For absolute encoders you need to connect a battery and 2 extra wires to request the position data when using the standard analog/pulse-train drives. And as I said above, the controller needs to be able to read the position data for the specific servo manufacturer.Quote:
Originally Posted by JAZZCNC
Now if you use EtherCAT drives, indeed you just need a RJ-45 cable between the drive and controller (but still need the battery). But you have 2 more problems:
- you need to actually find one of those rare EtherCat drives. Yaskawa for example doesn't sell them in the Chinese market. So you would need to go through an official reseller and pay $$$, or buy another brand: Omron / Panasonic / Mitsubishi / Delta / Estun...
- be prepared to spend weeks and write some C to make the controller talk to the drive (LinuxCNC in this case, the only one supporting EtherCAT).
Glad to hear this actually. Of course it is nice with speed and the non-existent noise! Who would not want 20m/min if they could have it. Anyway 10-15m/min will probably be enough for most small businesses and hobbyist (like me) as you said. I will let this thought about steppers sink for a while before I make any decision. The design is still not finalized anyway so no need to rush things.Quote:
Originally Posted by JAZZCNC
You said you are using Lichuan 8Nm 230Vac for the build with the ATC spindle and that you use Lichuan closed loop system nowadays for your build. I checked aliexpress and they are all either 2 phase or 3 phase. So they work with a 3 phase output but uses only 230V? I did not find any 8Nm steppers, but I found this one: https://www.aliexpress.com/item/3279...52606833P16XMw
Okay, I will research area more. I read somewhere that GT2 is supposed to be really good quality compared to the commonly used HTD 5.Quote:
Originally Posted by JAZZCNC
I agree about step/dir being simpler when drives handle position but not so sure that it's easier when your closing the loop back to the controller. Analog gives a little more control is my experience. But that said, my experience with servo's isn't massive and mostly with full closed-loop Analog controllers.Quote:
Originally Posted by jarjar
To be honest I think we are getting crossed wires a little here.! I know exactly what's involved with interfacing drives and wiring Absolute encoders etc.Quote:
Originally Posted by jarjar
My point was there's no more hassle using Absolute than incremental and there's actually less wiring required because you're not fitting home switches etc. Also if your using EtherCat or Bus type then there's even less wiring involved and less tuning involved because the controller and drives work closely together.
Also, I wasn't talking about Yaskawa Ethercat or trying to make Ethercat work with Linux or any other DIY controller. I'll be using an industrial Bus type controller with matched drives so i won't be needing to write any code etc.! . . . How long it takes to get up and running however will remain to be seen... .Lol
You can have 20mtr/min speeds with steppers if you choose the right drives/motors along with linear components, the 10x5 vertical machine I've been showing will happily whizz the gantry around at 30mtr/min.Quote:
Originally Posted by NordicCnc
Yes, those are exactly what I'm using for Z-axis with 12Nm on X&Y. I think the heading is an error, if you look further down at the spec you'll see it says 8Nm.Quote:
Originally Posted by NordicCnc
This size would be way overkill for your little machine thou. The secret to the speed with steppers, in general, is the relationship between inductance and voltage, but even more so with large motors which is why Mains powered drives work best.
It's Got nothing to do with quality, that's down to manufacturer and spec. HTD, GT2, etc is the tooth profile. GT2 is actually a modified HTD tooth profile which supposedly offers better handling of torque and speed than HTD.Quote:
Originally Posted by NordicCnc
You still need a homing switch to setup the absolute encoder reference. The only difference is that you don't need to home on subsequent power ups.Quote:
Originally Posted by JAZZCNC
Been told doesn't need a physical switch the system just needs to be calibrated with encoder offset for the home position which can be obtained through software..! . . . I will find out soon enough.Quote:
Originally Posted by jarjar
Some design progress has been made.
X-axis design
Attachment 27591 Attachment 27592 Attachment 27593 Attachment 27594
- L-shape gantry with 120x80 (heavy) Item profiles 1200mm long, with approximaterly 950mm travel length . The profiles for the L-shape are bolted together from the bottom. I plan to use aluminium plates as guides in the T-slots. Should these guides be fastened somehow or is it enough to insert them into the slots and shim away the clearance?
- High side gantry profiles with 120x80 (heavy) Item profiles, 160mm long. These are bolted to the bottom profile of the L-section, from the top of the bottom profile.
- 20mm aluminium gantry side plates, bolted to both the L-section and the high side gantry profiles. It is also bolted to the bottom plates, that will be mounted to the Y-axis bearing plates. The purpose of the bottom plates being separated from the Y-axis bearing plates, is to allow some adjustment later when squaring the gantry.
- 20mm HIWIN linear rails.
- 2010 ballscrew, 1150mm long.
- Delta 400W servo motor with a 2:1 reduction, to limit ballscrew RPM.
Attachment 27595 Attachment 27596 Attachment 27597 Attachment 27600 Attachment 27598 Attachment 27599 Attachment 27601
Y-axis design will continue from here!
I would use HGW bearings rather than HGH, they offer more support.
Got it, that is easy to change. Does this apply for the Z-axis as well?Quote:
Originally Posted by JAZZCNC
Yes and no, Yes if you have room but I only use them on X & Y as it can make the Z a little wide.Quote:
Originally Posted by NordicCnc
You don't need or want 6 counterbored holes in the lower gantry just use the 3 furthest away from the gantry side and the center front one, you can miss the out the center bolt through the gantry side or put it in but with short threads. Reason being the bolts going through gantry side clash with bolts and it's more important you get good fastening into sides so longer bolts needed. Between them, the gantry is going now were trust me.!
Also with the ball screw spacer plates pay careful attention to fastening bolts and that you can actually access them with BK bearing and screw in place because you'll need to adjust these on the machine when setting alignment etc.
Good notice! I have corrected that now and I will use shorter threaded bolts for the center ones (red arrow).Quote:
Originally Posted by JAZZCNC
Attachment 27604 Attachment 27605
Yes, I should be able to access those at anytime with current design.Quote:
Originally Posted by JAZZCNC
Attachment 27606 Attachment 27607
I have also replaced the guide carriages with the wider version, as you suggested.
Attachment 27608 Attachment 27609
Thanks for your feedback, I appreciate it!
I just noticed the size of the pulley and I'm assuming it's to scale.? Try to keep the pulley size small as possible to keep inertia low but at the same time making sure you have enough teeth engaged so don't get jumping teeth or premature wear. If you must use a large pulley then try to use an aluminium one, again to keep inertia low.
Yes, the pulley sizes in the pictures are 20T and 40T. How many teeth need to be engaged at bare minimum? I have not yet found any supplier (I am trying to find those pulley's with taper lock) so for now during the design phase, I went with some sizes I could find on Ebay.Quote:
Originally Posted by JAZZCNC
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20T and 40T is good, it's exactly what I use on one axis. Another handy calculator.Quote:
Originally Posted by NordicCnc
I had to deal with the same issue: finding clamping type aluminium pulleys, either HTD or GT3. From my researches those are rare beasts.
HTD taper-lock steel pulleys are relatively common, but add way too much inertia to be considered.
I found 2 options:
- CMT pulleys. The best but expensive, about $60 piece.
- Misumi, with separate taper-lock and pulley. Slightly less expensive, about $40.
Different manufacturers quote different numbers but I think it's roughly 6 teeth before you have to start lowering the HP rating they can handle.Quote:
Originally Posted by NordicCnc
However, your problem will be the smaller pulley size will limit the number of teeth based on it's Boss size and Motor shaft relationship. 20T / 40T sounds about right with a 14mm motor shaft, if it's 19mm shaft then you may have problems.!
Y-axis design
- 1600mm long, 160x80 (heavy) Item profiles will be used for the sides, onto which the linear rails are mounted. Travel length is approximately 1400mm.
- 1065mm long, 160x80 (heavy) Item profile is used for the front.
- 1065mm long, 80x80 (heavy) Item profiles will be used between the 160x80 side profiles. The base frame profiles are mounted together with front/end plates and 80x80 angles.
Attachment 27634 Attachment 27635 Attachment 27636 Attachment 27637 Attachment 27639
- The plates onto which the guide carriages and the ball screw nut housing are mounted are separated from the gantry. The purpose is to allow some adjustment later when squaring the gantry. It will also separate the aligning process of the Y-axis ball screw and linear rail from the gantry squaring process. This will make the aligning easier.
- 20mm HIWIN linear rails with wide guide carriages.
- 2010 ball screws, 1500mm long, with BK15/BF15 bearings.
- Double Delta 400W servo motors with a 2:1 reduction, to limit ball screw RPM. 20T and 40T timing pulley's will be used. Preferably with taper-lock mounting.
- Same servo motor brackets, BK/BF bearing spacers and ball screw nut housing concept are used as in the X-axis. Commonality and re-usability is the goal here.
Attachment 27638 Attachment 27640 Attachment 27641
Attachment 27643
- The spindle will have a 100mm overhang at when the Y-axis is at the end of the table. The purpose is to be able to mount work pieces vertically, for dovetail machining.
Attachment 27644 Attachment 27642
- The table surface I am not sure about yet. Either I will install a HDPE sheet or and MDF spoil board.
- The complete machine will later be mounted to a sturdy metal bench/frame. Adjustable feet will be used.
Attachment 27645 Attachment 27646
Originally I intended to have the Y-axis linear rails side mounted, to make the footprint as small as possible and to protect the rails from dust and chips. I was informed that alignment is significally harder with side mounted rails, which is why the rails are now top mounted.