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Author Topic: Mach4 Spindle At Speed, Spindle Zero Problem  (Read 8922 times)

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Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #80 on: December 26, 2017, 05:30:15 PM »
Hi Craig,

As much as i read from their web site they say its special designed servo-induction motor and it has high positioning accuracy, it is driven by a servo drive so i dont think its a regular encoder mounted induction motor, i think they put permenant magnets in it somehow, as u know there are special motors nowadays like magnomatics.. so they modified the induction motor and make an hybrid servo-induction motor as they state.

Also i saw some videos on youtube from ctb servo, by the way they also say it has an holding torque of 17.5Nm at 0 speed of 5.5kw 12000rpm motor so it cant be just a regular induction motor.

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #81 on: December 26, 2017, 06:12:44 PM »
Hi Hakan,
believe it or not it COULD be an induction motor. If you've done any reading about Field Oriented Control then you will realize that a permanent magnet
motor differs from an induction motor only by the addition of quadrature phase flux to the rotating flux vector. A Google search and look out for some fascinating
videos from Texas Instruments. They get right into sensorless vector control as well, a control engineers wet dream!

Having said that a permanent magnet rotor is still more likely especially as neoydium magnets are now so cheap. There is a blurring here of naming.
Strictly any rotor which is magnetized by 'induced' currents is an induction or asynchronous motor whereas any permanently magnetized (or magnetized by a DC
current in a wound rotor supplied by slip rings) is called a synchronous motor but also called a brushless DC motor or an AC servo.

A brushless DC motor seems like a contradiction in terms. The rotor is permanently magnetized. The stator windings around the outside are required to provide a
rotating flux vector in order to rotate. An electronic control turns DC on and off to the windings to do that. If you think is sounds like a VFD its because they ARE
very similar. What differs with a VFD and a genuine servo drive is that the angular position of the flux vector is under closed loop control with encoder feedback
with a servo drive but not a VFD.

The simplest of switching systems is called trapezoidal control and can be enacted even without an encoder. These are commonly called brushless motors
and are particularly popular with radio control and modellers. The motion is a bit 'lumpy' though.

The other main way is 'Sinusoidal Pulse Width Modulation'. It requires an encoder (for postion control anyway) and results in very smooth and accurate motion
ideal for servos. These are widely called AC servos. The required computing power necessary to do the field oriented control calculations were expensive
back in the 90's but nowadays a 32 bit Microcontroller with single cycle floating point calculation and many many MANY hardware periphials are dirt cheap.
Consequently AC servos are the entry standard now.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #82 on: December 26, 2017, 06:31:55 PM »

Thanks for the detailed explenation Craig, i didnt understand the half of it  ;D but u say an induction motor may have 17.5Nm torque on the shaft in 0 speed? if so my induction motor sucks because it has 0Nm at 0 speed  ;D

Regards,

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #83 on: December 26, 2017, 06:40:21 PM »
Hi Hakan,
that can't be correct....if it had zero torque at zero speed when you turned it on it would never start to rotate.

Its certainly true that induction motors have poor and poorly controlled torque at start up and over the years vast sums have been spent
to improve that basic limitation.

Induction motors are great and with VFDs remarkably speed flexible. If you want position control they suck.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #84 on: January 10, 2018, 06:01:12 PM »
Hi Craig,

It was not of course 0 but what i meant was it was very close to zero, actually what i meant was this;

https://www.youtube.com/watch?v=fzHWudx2wgU

but the strange thing is, this happens my case in the opposite way. When i adjust the vfd as vector drive there is no torque in low speed, but when i change it to v/f mode there is torque and u can not stop the shaft with hand.

As u suggested before i gave up from the idea of intalling an encoder at the end of the shaft, but now if i want to implement the ATC function i need to align the shaft of the spindle to an angle.
The reason is the drive dogs on the tip of the spindle has to go in to a slot in the bt40 holder(at the atc side). So to do this i need to stop the spindle shaft at a point lets say parallel to x axis.

As u know Delta Vfd s has encoder cards PG01 i think or something like that, i thought matbe i install an encoder on the shaft and connect it to vfd through this encoder card it may be possible to stop it at a count number of the encoder. For example if i is 1024 pulse per turn i can program the vfd to stop at pulse 512 in every stop command. I asked this to the Delta support in here they say it is not possible on VFD-E series but it is possible with VFD-C2000 series. But in VFD-E booklet it says u can make speed and position control with this card so i am confused.

do u know anything about this? i attached the related portions of the booklet.

If this is not possible according to u too, can u think of anyway other than the mechanical option?

Thanks in advance.

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #85 on: January 10, 2018, 09:25:49 PM »
Hi Hakan,
to my knowledge you cannot use a VFD either V/F or sensorless vector mode to achieve position control. I don't think an encoder will help, my Delta VFD can use
an encoder, Delta call it a pulse generator, to get really good speed control but its still not capable of position control.

You need a decent AC servo and drive. I know they are expensive but once you get one you'll never look back.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #86 on: January 11, 2018, 07:07:52 AM »
Hi Craig,

I will go with servo option next time for sure but in this machine i need to solve it somehow, thanks anyway.

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #87 on: January 18, 2018, 08:45:34 PM »
Hi Hakan,
I just had a thought that may help you index your spindle. My VFD has a jog button, you can program it
turn the spindle very slowly. I've never used it. If you had an index switch on the spindle which operated
when the drive dogs lined up it might work.

1) Set an output to drive the jog terminal of your VFD
2) wait until the index switch activates
3) Reset the output

Craig
My wife left with my best friend...
     and I miss him!

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Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #88 on: January 18, 2018, 10:26:28 PM »
Machines with tool changers and induction motors on the spindle use a spindle key lock.  The spindle is rotated slowly at low torque and the key lock is engaged.  When the key lock drops into the notch on the spindle shaft, the VFD is turned off.  So it is a pure mechanical orientation. 

Steve
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #89 on: January 18, 2018, 10:32:27 PM »
Hi Steve,
kool, the jog feature would allow the spindle to turn at a slow enough speed that the lock would be effective.

Craig
My wife left with my best friend...
     and I miss him!