Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: BIGWING on March 16, 2011, 09:56:24 AM
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I have an Emcoturn 120 3 ph cnc lathe am I am looking to convert to 1 ph Mach3. To make the project more manageable it is my intention to split the overall project into smaller lumps, so for the moment I am concentrating on the Spindle drive.
My electrical knowledge is very limited so any help from the forum would be greatly appreciated particularly at this early stage to stop me going off in the wrong direction.
Existing spindle setup
The current spindle drive is a 2.6kw DC Siemens motor (GL5104-OEZ40-6JU7-Z)
with integrated 3ph cooling fan. Direct belt driven (see photos) output speed 150 -4000 rpm max torque 17.6 NM and belt driven encoder (approx 300 slots)
(http://C:\Documents and Settings\admin\Desktop\lathe\spindle.JPG)
(http://C:\Documents and Settings\admin\Desktop\lathe\belt drive.JPG)
(http://C:\Documents and Settings\admin\Desktop\lathe\torque.JPG)
(http://C:\Documents and Settings\admin\Desktop\lathe\cooling motor.JPG)
(http://C:\Documents and Settings\admin\Desktop\lathe\encoder 54.JPG)
(http://C:\Documents and Settings\admin\Desktop\lathe\encoder assy.JPG)
I have noticed on the forum that a Parker ssd 514c unit would control this motor but I had a look at the manual and it didn’t look particularly straightforward also not sure how I would tackle cooling fan. Also not sure if this motor to powerful and costly to run for hobby needs.
Question 1 Do you think it is worth persevering with this motor ?
I was thinking of saving money by going for a smaller motor say 1.5 kw with ac inverter
Question 2 Is this a false economy ? ( I want to cut threads and not sure about torque level at slower speeds)
2,4,6 pole motors !!! I am not sure what would be better for my application relating to torque, running cost and surface finish
Question 3 For average working speed say 1500 rpm. Is it better to get a faster motor slowed down by inverter drive or slower motor speeded up by inverter?
I have noticed a massive price difference for ac inverters of the same power rating
as much as 300% the more expensive quoting vector control
Question 4 For my application is this extra cost justified? Does this just give more accurate speed control or are there any torque/ heat implications particularly at lower speed?
I have been looking at various breakout boards on the internet to see how the spindle controls are hooked up and many show inverter connections going straight back to BOB. But I have also seen speed controllers advertised and connected up to similar ac inverter drives. Eg
http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=303
Question 5 What are the benefits of these controllers?
The lathe comes with its (very well made) own spindle encoder (see photo) approx 300 slots
Question 6 Is this too many slots for mach3 to handle and does single slot produce accurate threads?
Not sure what voltage output is for this encoder or of wiring details.
Question 7. Do you think I should change this for new or can anyone help with info?
Any comments from the forum would be greatly appreciated. Even if you only have answer for one of the questions. It all helps
Cheers George
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Do you have a link to the specs of the motor or do you have the specs?
Servo spindles are the best so I would try hard to keep it.
Do you have a drive for it and if so do you have a link to the spcs.
Hood
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Hi Hood
sorry having a few problems trying to get photos loaded. will try again now.
I don't think it is a servo (but not sure) as encoder (item 54 in photo) totally separate
I do have electronic manual for motor but may have to take copies of some of relevant pages
as I think it is very big file to upload. I will wait to see what you think after viewing photos.
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here is the link for the parker controller recommended. The existing drive is I believe of emcos own design and integrated into the control panel ( 20 years old and not supported now)
http://www.inverterdrive.com/group/DC-Thyristor-Drives/SSD-514-8A-Eurotherm-Shackleton-Rapier-Drives-540-/default.aspx
just in case not clear from photo encoder belt driven below main spindle
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here is the two other photos
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Here is motor manual (not as big as I thought)
Siemans dc motor GL5104 NLF6 ( GL5104-OEZ40-6JU7-Z)
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I would certainly try and keep that motor, look at the torque, it is constant from zero rpm up to rated speed, you will not get that with an induction motor and VFD. If you do go with induction/vfd then I would say tripple the KW at least.
The manual attached doesnt really say much from what I can see and I have searched Siemens site but the model you quote doesnt seem to bring up any info. Can you take a pic of the nameplate on the motor, that might help find more ino.
Hood
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Hi Hood
photos not particularly clear so also added word document with what I think they say.
what do you think would be the best way to handle integrated cooling motor as I need 1 ph supply.
!) change motor to 1 ph
2) Can parker contolller control this as well? (may be stupid question)
3) get separate controller for this?
and how do you think it should be controlled ie
1) temperature
2) always on when lathe switched on
3) always on when spindle motor running
4) other
cheers George
ps will try internet search to see if I can get any more info motor
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Just cant seem to find any Siemens specs for the motor but it does seem like its a DC servo, its high voltage though so I think you will likely struggle to find something single phase to control that :(
The Parker on single phase is only 180v DC output from the quick look I gave the page, that would likely get you about 700rpm.
One option may be a rotary phase convertor so that you can get the 415v three phase (assuming you are UK)
If you do decide to use a normal induction motor and a VFD then I would look at something twice the Kw of the original motor as you will lose torque at low speeds, and that is where you want it. This is just from my own experience from VFDs so maybe things are better now as my VFD was maybe 10yrs old.
Other option may be to try and find an AC servo motor and drive, I use AC Servos that I picked up on eBay but they are scarce in the UK for the type I use.
Hood
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Hi Hood
thanks for that
before I dismiss it totally I will contact siemens directly to see what they would recommend to control it. if anything
will post reply
Cheers George
PS yes UK
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Hello.
Did you successfully Retrofit your Emco Turn with mach3?
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Hi,
since this thread was started (2011) AC servos have become MUCH more common, including a good supply of second hand
units on EBay. Trying to preserve old DC motors is becoming an expensive proposition despite otherwise good performance.
AC servos offer at least as good torque characteristics and a VASTLY improved range of control modes, including indexing,
torque, velocity and position modes.
Induction motors and a VFD are pretty good, especially on a budget but a servo (AC or DC) will have torque to zero speed
for which an induction motor will overheat rapidly.
Craig
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Thanks a lot for the answer… You are right AC servos have become more common nowadays
I am working retrofitting two Emco Lathes.
Thanks
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Hi,
I'd had little to do with AC servos until I bought one second hand (1.8 kW Allen Bradley) for use as a spindle
motor for my mini-mill. It has been a revelation. I have from University days been familiar with the great torque characteristics
of DC servos, but its the hugely increased range of control options that put DC servos into the shade.
Servos, either AC or DC, have superb torque density, that is they produce more torque for a given size motor than
an induction motor. They can be exceeded, but only at low speeds by large steppers. In addition they have superb
overload characteristics, they continue to work in overload until the onset of overheat whereas induction motors once they hit
their stall torque, seldom more than 50% rated, stall completely. Likewise hit the torque limit of a stepper, reducing at increasing
speed, and it stalls.
Yet another advantage of AC servos, not often used in servo drives, but extensively used in brushless spindle motors is 'field
weakening'. Its where you can enter a mode that induces the rotating magnetic field by the stator has its normal quadrature
(torque producing) component but also an anti-parallel component which in effect redues or 'weakens' the permanent magnetic
field of the rotor and thereby reduces the back EMF allowing for higher speed operation with the same power supply.
You may have noted that high end production CNC machines will list traverse speeds say of 50m/min but max cutting speeds
of 30m/min. This is the classic means of utilizing field weakening. In the field weakened condition the servo can spin faster
albeit at reduced torque but sufficient to get great traverse speeds. When the servo reverts to its normal non-field weakened
condition it regains its full torque to produce its maximum cutting speed. Great flexibility can be achieved with field oriented
control that is just not possible with DC servos.
Craig