Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: ashish on October 01, 2008, 07:28:51 AM

Title: servo selection.......
Post by: ashish on October 01, 2008, 07:28:51 AM
Hi all,
Can you guys help me out with servo selection  for milling machine.
I have an old milling machine and i want to fit it with mach 3 along with servos..............for better stability.
I have two cheap options for servo
                                                 A) Delta Electronics servo
                                                 B) Yashkawa  servo
I guess 4Nm will be good enough to start with but i am not sure what PPR to choose for encoder. 2500 PPR is the minimum available encoder resolution. And its a 3000 Rpm motor.
What is the max. encoder frequency that a mach3 can handle.
Would it be more accurate to use G100 with 600Mhz PIII  laptop  instead of high end desktop PC .

Thanks
Title: Re: servo selection.......
Post by: HimyKabibble on October 01, 2008, 10:37:35 AM
I have just CNC'd my knee mill using servo motors from www.homeshopcnc.com.  They have 500 line/2000PPR encoders.  Mach3 never "sees" the encoders - they are only connected to the servo controllers (Gecko or whatever).  I could not be happier with the way my mill now works.  It's fast, powerful, and accurate.  The motors have enough torque to snap off a 1/2" endmill without losing position!  I used Geckos G320s, and a SmoothStepper (which was MORE than worth what it cost!), running Mach3 on a lousy 540MHz PC.  The servos are "geared down" 2.5:1 with GT2 timing belts.  (BTW - I can provide CAD drawings of the belt reducers I designed if you like - they are easily adaptable to other machines by changing the adaptor plate).  My power supply is 70V/20A.

Regards,
Ray L.
Santa Cruz, CA
Title: Re: servo selection.......
Post by: Hood on October 01, 2008, 03:47:51 PM
2500ppr will mean Mach needs to put out 10,000 pulses per rev. If you dont have electronic gearing and are using the parallel port you are looking at approx 1350mm/min (asuming 5mm ppitch). There  is a device called the Smooth Stepper (as Ray has mentioned) which pulses externally from the computer and it allows pulses up to 4MHz so it is perfect for high count encoders. I have 2000 line encoders and using 1:2 electronic gearing in my drives I was limited to 3500mm/min on my lathe, now with the SmoothStepper I am 13,200mm/min and could actually go more than twice that speed if the motors could but as the lathe is heavy 13m/min is quite fast enough.

Hood
Title: Re: servo selection.......
Post by: polaraligned on October 01, 2008, 06:24:46 PM
Go with the minimum encoder count available.
Use a servo drive that has "electronic gearing" such as the
G340.  (Not the best, -but the best bang for the dollar)
Save your money and don't bother with a smooth stepper.
Get a 1.8 Ghz or better computer running XP or XP pro.
Use the parallel port to drive the servos (through a break out board)
and you will get all the rapid speed a knee mill can handle.
Forget the G100.....99.5% of all mach users use the parallel port. 
I just picked up a P4 at 1.8 ghz and 512mb ram with 40 Gb hard drive
for $199.
I use a similar machine on my BP series 1 with no issue. 

Scott



Title: Re: servo selection.......
Post by: Hood on October 01, 2008, 06:32:35 PM
Scott, what do you reckon "all the rapid speed a knee mill can handle." is?
just curious

Hood
Title: Re: servo selection.......
Post by: polaraligned on October 01, 2008, 07:21:10 PM
Original poster is obviously not going to use the machine in a commercial
environment.  If he was a good used VMC would be a much better
 than an "old knee mill"

He can get about 220 ipm rapids with the PP and a divide by 4 on the drive.
This would take the table 18" in 4.9 seconds. 
Are his ballscrews designed for that kind of rotational inertia?
Does he even have ballscrews?  Was his machine designed
to take high speed rapids?

Speed is nice to oooh and ahhh the bystanders but how much time does
it really save?  Very little unless you are making parts day-in and day-out.

I set my BOSS to 80 IPM rapids and I program so I spend my time cutting
parts and not rapiding.

A router, plasma, etc would be a different story as you are moving a
lower mass and usually moving it a much larger distance.

Scott

Title: Re: servo selection.......
Post by: Hood on October 01, 2008, 07:35:34 PM
My Boss is 2500mm/min (100IPM ) and that is plenty fast for that but the Beaver is in a different league and 10,000mm/min  is what will be used on that. Dont know what machine the OP has but just when he mentioned he was thinking of 4Nm Yaskawa I presumed it was  probably more than just a Boss or similar, but maybe not.
Hood
Title: Re: servo selection.......
Post by: polaraligned on October 01, 2008, 08:26:06 PM
What kind of travels do you have on the Beaver?

My next retro is a Series 2 CNC.  15" x 30" travel,
huge box ways, table never overhangs saddle, 5000#.
Pretty much as close as a knee mill can get to a VMC. 
The iron is fully rebuilt and I am heading into the controller
now.  I don't know if the SmoothStepper is worth the
extra money for this machine.   So many machines running solidly with
just the PP.  I ordered Granite drives for this one.  Geckos are to
"hobby' for me.  They run my Series 1 Boss-  but not without
occasional problems.

Scott

Title: Re: servo selection.......
Post by: ashish on October 02, 2008, 02:04:45 AM
Dont know what machine the OP has but just when he mentioned he was thinking of 4Nm Yaskawa I presumed it was probably more than just a Boss or similar, but maybe not.
Hood


Thanks for all your valuable feedback.

Dear Hood I got two old cnc machine made by (Kirloskar Indian manufecturer) Its 10 yrs old actually the system was fitted with their proparitry hardware n now they don't support for it any more. Its been laying at my frriend factory n he was abt to retrofit it with Siemens 810 cnc  ( he is in cranes and hoist manufecturing business.).
So i came up with my idea of turning this one machine into mach3 Pro CNC. And let it stand far above Siemens 810 in terms of features and performance.

This mach3 replacement has to be industrial grade so, i go with yashkawa coz its available in india.

The system integrator told me that this servo have simulated encoder o/p. That means for 2500 PPR i can have any PPR for mach3 from servo itself.

Once again thanks alot guys.
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 02:34:45 AM
What kind of travels do you have on the Beaver?
16 X 32 travels and around 2000 - 2500Kg if I remember correctly. Has Box ways and a motor on the knee which I am planing on fitting with a servo at some point. The quill is 4 inch dia 40 taper with 6 inch travel.


Thanks for all your valuable feedback.

Dear Hood I got two old cnc machine made by (Kirloskar Indian manufecturer) Its 10 yrs old actually the system was fitted with their proparitry hardware n now they don't support for it any more. Its been laying at my frriend factory n he was abt to retrofit it with Siemens 810 cnc  ( he is in cranes and hoist manufecturing business.).
So i came up with my idea of turning this one machine into mach3 Pro CNC. And let it stand far above Siemens 810 in terms of features and performance.

This mach3 replacement has to be industrial grade so, i go with yashkawa coz its available in india.

The system integrator told me that this servo have simulated encoder o/p. That means for 2500 PPR i can have any PPR for mach3 from servo itself.

Once again thanks alot guys.

 I dont have Yaskawa drives but use similar style Giddings and Lewis  drives with AC Servos and the encoders are 2000line. As long as the Yaskawa will accept Step/direcion signals you are fine but to get the full benefit you will need a SmoothStepper. I think Yaskawa call the Step/Direction signals something like Pulse/Signal.  The Yaskawa will have electronic gearing but personally I feel its not a good thing for a CNC machine as the higher you set the gearing the more cogging you will get at lower speeds. On the lathe I at first had the gearing set to 1:4 but had to turn it down to 1:2 and even that had cogging at crawling speed now with the SmoothStepper I dont need any electronic gearing and  still I am only using about 1/4 of the pulse rate its capable of.
 The lathe Has 10Nm motors amd the Beaver mill has 5Nm motors on Y and 3Nm on X and Z.
 You dont need encoder output from the drive for Mach, it is the other way round, the drive needs to accept Step/Dir in. Mach is open loop but the drive closes the loop.

Hood
Title: Re: servo selection.......
Post by: ashish on October 02, 2008, 02:48:37 AM
what about using mach in closed loop. Along with the 1:10 gearbox  (bonfiglioli gearbox)
I guess it will improves the performance.

Well yashkawa servo accepts 200kps maximum.
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 03:08:23 AM
In the future closed loop may be a possibility with Mach  but at this time Mach is open loop. At the moment the servo drives close the loop and they will attemp to get the motors to the position that Mach tells them to go, if for any reason they do not get there then the drives will fault and you can send this fault signal to Mach and it will halt outputs from Mach.
 On my drives I have the following error set to 20 counts, that equates to 0.0125mm of axis travel and I have not had a fault due to that yet :)

Not sure where you are wanting the gearbox, I have all of my motors connected direct with no reduction, with 2000 line encoders that  is 8000pulses per rev from Mach so the resolution for me is 5mm pitch / 8000 = 0.000625mm (0.0000246 inch) ,  dont think you need any better than that ;)

Hood
Title: Re: servo selection.......
Post by: ashish on October 02, 2008, 03:35:30 AM
Hood
0.000625mm is more than enough but let me check what a siemens 810 is capable of.
What CAM and CAD software u r using.
I got Solid Works 2005..............but looking for freeware or open source CAM package.
I want to use gear box with tool indexer......................that would be last mod for the machine but its better to get all things in budget before.
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 06:28:12 AM
Your resolution would actually be more than that as you have 10,000 pulses per rev so presuming you have 5mm pitch ballscrews then it would  be 5/10000 = 0.0005mm (0.0000197")

 Not sure what you are meaning by "Well yashkawa servo accepts 200kps maximum."

Hood
Title: ..
Post by: ashish on October 02, 2008, 07:01:08 AM
Not sure what you are meaning by "Well yashkawa servo accepts 200kps maximum."

That means 200,000 pulses per second is the pulse rate which servo can accept for the position velocity.
200,000 pulse per second = 3000rpm
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 07:11:12 AM
OK but 200KPS is not 3000RPM, you have 2,500 line encoders so that is 10,000 pulses per rev as far as Mach is concerned. So 3,000RPM = 50Revs per second, multiply 50 x 10,000 pulses and that equates to 500KHz (Kps as Yaskawa are calling it)
 The only thing is there is a possibilty that Yaskawa, because they state Kps rather than KHz , so their 200kps would actually be 800KHz and in that case you will be fine.

Hood

edited with right number of revs per secong ;D
Title: Re: servo selection.......
Post by: ashish on October 02, 2008, 09:16:26 AM
can i ask u what kind of isolator u have used between servo's and lpt port.
coz yashkawa servo accept's 24vdc npn logic.
Title: Re: servo selection.......
Post by: HimyKabibble on October 02, 2008, 10:50:12 AM
OK but 200KPS is not 3000RPM, you have 2,500 line encoders so that is 10,000 pulses per rev as far as Mach is concerned. So 3,000RPM = 500Revs per second, multiply 500 x 10,000 pulses and that equates to 500KHz (Kps as Yaskawa are calling it)
 The only thing is there is a possibilty that Yaskawa, because they state Kps rather than KHz , so their 200kps would actually be 800KHz and in that case you will be fine.

Hood

Hood,

    3000 / 60 = 500?  Looks like the ol' Casio may be ready for new batteries....  :-)

Regards,
Ray L.
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 12:20:41 PM
Hood,

    3000 / 60 = 500?  Looks like the ol' Casio may be ready for new batteries....  :-)

Regards,
Ray L.

oops, bit of a typo there but the final figures are correct I think ;) just put an extra zero in, I have an excuse, I was running the mill, the lathe and also drawing a ciorcuit board up while I was working it out and replying , well thats my story and I am sticking to it ;D

Hood
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 12:24:48 PM
ashish

I have various means of doing that, first thing is my Step/Dir inputs to the drive are 5v and I would imagine the Yaskawas would be the same, so no need for anything there. The rest of the I/O on the drive is either through a PLC or things like limits are through relays to the PC.

Hood
Title: Re: servo selection.......
Post by: HimyKabibble on October 02, 2008, 01:25:16 PM
Hood,

 3000 / 60 = 500? Looks like the ol' Casio may be ready for new batteries.... :-)

Regards,
Ray L.

oops, bit of a typo there but the final figures are correct I think ;) just put an extra zero in, I have an excuse, I was running the mill, the lathe and also drawing a ciorcuit board up while I was working it out and replying , well thats my story and I am sticking to it ;D

Hood

Hood,

    Doing all that, it's a miracle you didn't spill your Scotch!  :-)

Regards,
RayL.
Title: Re: servo selection.......
Post by: Hood on October 02, 2008, 03:14:37 PM
no chance of that :)

Hood
Title: Re: servo selection.......
Post by: ashish on October 03, 2008, 04:09:57 AM
ashish

I have various means of doing that, first thing is my Step/Dir inputs to the drive are 5v and I would imagine the Yaskawas would be the same, so no need for anything there. The rest of the I/O on the drive is either through a PLC or things like limits are through relays to the PC.

Hood


Just through the manual again n found that they have two options for driving the position pulse.
a) line driver.........it uses 24vdc power from drive itself n a current limiting resistor.
b) Open collector ............its external supply n different resistance value for optocoupler.


I guess B is for 5Vdc signal. Should i go for it.
Title: Re: servo selection.......
Post by: ashish on October 03, 2008, 04:12:09 AM
here is the details i found in the manual
Title: Re: servo selection.......
Post by: ashish on October 03, 2008, 04:18:49 AM
Hood,

Can we use HID device or Joystic Port with Mach3 ....for analouge input signals. Or we just have MODBUS for external devices.
Title: Re: servo selection.......
Post by: Hood on October 03, 2008, 08:44:02 AM
Think the only  analogue inputs at the moment is ModBUS, hover the PoKeys should hopefully have them shortly. Art is working on a plugin to take adavantage of MPG inputs and Analogue Inputs.

Looks like you should be able to use the 5v for the Step/Dir inputs to the drives, would just need a suitably sized current limiting resistor.



Hood
Title: Re: servo selection.......
Post by: ashish on October 03, 2008, 10:41:19 AM
Think the only analogue inputs at the moment is ModBUS, hover the PoKeys should hopefully have them shortly. Art is working on a plugin to take adavantage of MPG inputs and Analogue Inputs.


There's and open source diy available.................... http://1010.co.uk/avrhid.htm l..........................if this goin to work with mach, don't u think we can have ProPad kind of stuff added to our Mach.
For plugin ......its up to Artsoft how much they can support n how many users want it customised.

Should we get this on FEATURE REQUESTS

Thanks for confirming ster/dir issue.........let me hard-wire them this weekend
Title: Re: servo selection.......
Post by: Hood on October 03, 2008, 11:21:17 AM
Your link seems dead. If you are capable of writing a plugin then you can use almost anything you want with Mach, I believe there is a SDK for writing plugins.

Not really confirming that you can use 5v Step/dir inputs but certainly looks like you can from the pics you posted above.

Hood