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Author Topic: Mach4 Spindle At Speed, Spindle Zero Problem  (Read 9105 times)

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Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #70 on: December 26, 2017, 12:47:35 PM »
Hi Craig,

I am back  ;D

the spindle at speed function we(you) implemented to Mach4 works just fine machine acts more like a professional machine and now i decided to upgrade the spindle to more professional one i ordered one BT40 ATC belt driven spindle from CELLS.I remember u saying something like that i can add an encoder to the spindle, so that Mach4 will know the exact rpm of the spindle. This will also help in other functions like threading etc.

I searched some suppliers and found an encoder which has 12000rpm max. speed but 100ppr as resolution(u can see details in the attached document), i have couple questions to u since u know these technical stuff better than me;

- do u think this encoder is suffice for Mach4 in means of ppr?
- what output type(NPN, Voltage Output, etc) should i choose?
- what output phase(A, A+B, etc.) should i choose?

to make this work with Mach4, and i have PMDX126+ESS setup also using PMDX107 board for pwm spindle control.

Thanks in advance,

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #71 on: December 26, 2017, 01:28:30 PM »
Hi,
you don't really need an encoder. Mach requires an index pulse, that is one pulse per revolution, and it ca calculate the rpm from there.
Many encoders have the normal quadrature A and B channel but often an index pulse as well, sometimes called I or Z signal. If you wish to fit
such an encoder go to it but realize that you'll only be using a small fraction of it capabilities.

I suggest a small Hall sensor and a small magnet glued to the spindle shaft.

http://nz.element14.com/honeywell/ss443a/sensor-hall-effect-140g-unipolar/dp/3111507

A suitable example.

Note that Mach is not a closed loop controller, it can use an index pulse to calculate the actual speed but it does not use that speed to adjust the PWM to your target
speed. You can with a bit of clever programming make it do that but the response is very slow. There are a number of external motion controllers that enact closed loop
control, good ones tend to be expensive. Just recently Warp9 have added a simple PID closed loop control to their Ethernet Smoother Stepper. I haven't used it yet but
it would be ideal for this application. Do you have or use an ESS?

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #72 on: December 26, 2017, 01:45:46 PM »
Hi Craig,

Yes i am using an ESS with my current setup, i installed the new plugin to test the backlash compensation and i saw some new boxes added to spindle tab, is that PID closed loop control function?

As far as i test it its backlash compensation does not work yet i dont know why but as the movement of the axis keeps longer the compensation gets bigger and it results an error on the axis isntead of fixing it. I have 0.003mm backlash because of the ballscrew on one of the axis and i coulnt be able to fix it with ess backlash compensation, this is another topic but i am not sure that spindle PID control works as u said it needs to be tested.

The reason i wanted to use this encoder: it is more suitable to my setup in means of assembling, it has 22mm bore so spindle motor shaft output is 22mm in diamater at the back of it, it will be more compact and professional looking in this way  ;)

Do u think encoder can be connected with ESS PID function and can be used in getting the exact rpm and also in threading type processes?

Hakan

Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #73 on: December 26, 2017, 02:05:55 PM »
Hi,
by all means use the encoder, its way more expensive, but that's your call.

The ESS PID function at this time accepts one pulse per revolution, ie an index pulse. Provided the encoder has an index pulse it will work.
Andy at Wapr9 has suggested that at a future time a multi pulse per rev PID controller will be enacted but when?

You may have noted that the backlash compensation feature of the ESS is only a month or two old and is still in its Beta test phase. If its not working correctly
get onto the Warp9 forum, Andy needs all the feedback he can get to perfect backlash compensation.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #74 on: December 26, 2017, 02:26:27 PM »
Hi Craig,

I know its expensive but as u said for future implementations it will be ready, so as far as i understand i should ask to manufacturer that the encoder should provide an index pulse which is 1 pulse per revolution it will be usefull to zero the spindle like an axis. I will implement some other features which i can use that indexing function also so its a good idea, i am not sure if they provide it in incremental encoders but i will ask..

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #75 on: December 26, 2017, 02:36:34 PM »
Hi,
if the encoder doesn't have an index pulse don't waste your money, it wont't work.

Our previous conversations in the thread were about a VFD. A VFD is not really position capable.  For that you need a servo, in which case the encoder is built
in and you won't need PID of the ESS, the servo and controller offer way way WAY tighter control than that.

If you want an indexing or co-ordinated spindle a VFD and induction motor are not the right choice. Is there any point in trying to provide 'future expansion'
when the existing motor technology wont manage it?

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #76 on: December 26, 2017, 03:02:00 PM »
Well Craig,

Once again u are right.

The thing is old spindle could not do steel, i installed it to test the positioning and machining accuracy of the machine on Aluminum but i couldnt stop my self since the machine body is strong i tried it on steel so spindle couldnt take it  ;D

so i had to change it with lowest cost possible, i sent it back to manufacturer and engineer in there is a good guy and he made me a new induction motor with 4 poles 400mhz 12000rpm specs. and i paid 50 bucks for that. As u know i had 4kw delta inverter so no need to change the inverter i already got the motor and tested it. Its better than the old one, bigger motor 130x130mm and i will use it to drive the CELLS spindle. So at the beginning i thought to go with Servo motor but it would be more expensive and as u know servo motor max. speed is about 3000rpm. I will use this induction motor with direct coupling to the belt driven spindle because my Zth axis has no space for belt setup.

As u say for now best way is to use the hall effect sensor with a small magnet on the output shaft, i think ESS PID should work with that as u suggested. Any programming needed to make it work?

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #77 on: December 26, 2017, 03:27:39 PM »
Hi Hakan,
no special programming that I know of.

You were lucky to get a new motor that cheaply. I have a much smaller (750W) German made spindle and a Delta VFD capable of 24000 rpm.
I thought I would be able to do steel to....didn't work. The problem with high speed spindles is they have very little torque and so spinning a tool slowly,
as is required by steel, is just their weakest point.

To cut steel and stainless I made my own spindle with a RegoFix cylindrical ER25 tool holder, ABEC7 angular contact bearings and a second hand 1.8kW
Allen Bradley servo and drive. The servo is rated to 3500 rpm and I have it direct coupled to the toolholder. Rated torque of 6Nm and temp overload of
18Nm. Works really really well in steel and stainless. My little mill can't really handle the torque but man sure makes chips!

One of the advantages that come with using a servo is that they are superbly position controlled so I can do rigid tapping for instance. Speed control when
you have such good position control is trivial. Despite the servo and drive being second hand all up its cost about $2000 to make it, not cheap. I did use
absolute top class toolholder and bearings which added to the cost considerably.

Excepting indexing and rigid tapping your spindle will work well. I think the cheap way of a Hall sensor and a tiny button magnet are the way to go.
Save your dollars for a servo type spindle in years to come.

Craig
My wife left with my best friend...
     and I miss him!
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #78 on: December 26, 2017, 04:30:56 PM »
Craig,

I think best way is to get a high torque 3000rpm servo motor and connect it to the spindle with 1/4 ratio pulley so it will have less torque but spindle will turn in 12000rpm and u can have absolute control of it. But in my current setup i can not make it because of the shape of the Zth axis, in next machine i will do that altough pulley and belt setup has its negative sides like u can not get smooth surface because of the belt vibration..

Or better than servo-pulley setup i can buy one of these new type high torque high rpm induction servo motors  ;)

https://ctbservo.en.alibaba.com/product/60413434018-802808822/CTB_7_5kw_CNC_milling_servo_spindle_motor.html?spm=a2700.8304367.prewdfa4cf.2.49792a76dr9rjN

Hakan
Re: Mach4 Spindle At Speed, Spindle Zero Problem
« Reply #79 on: December 26, 2017, 05:17:57 PM »
Hi,
high power, high speed induction motors certainly make good spindle drives but they are not so good at position control.

An induction motor relies on the rotating magnetic field of the stator windings being faster than the rotation of the rotor, the difference, called slip
is what 'induces' current in the squirrel cage rotor and how induction motors get their name. If it were necessary to back the rotor up half a turn say,
as in a position control application, the field windings have to reverse and sufficiently so that there is enough slip for the rotor to be magnetized. If the rotor
overshot then the field windings would have to reverse again including the required slip. Induction motors are not good for position control.

If the rotor is permanently magnetized as they are in servos there is no need for slip. The rotor is synchronous with the field windings. The resulting position
control is way tighter than an induction, also called asynchronous, motor. Additionally there is no requirement for the field windings to supply the induced
rotor current. As a consequence permanent magnet servos are smaller than induction motors for the same power. Further the torque characteristics of a servo
are linear with current and extend to zero rpm. You can use a servo as a torque motor, many thousands are used in this manner in printing presses which is
possible but harder to ensure than with an induction motor.

Induction motors are simple and cheap but if you want position control they are not the right way to go.

There is a warning to, most induction motors are designed for 50-60 Hz line frequency. A motor driven by a VFD has a much higher insulation requirement.
If you use an ordinary induction motor on a VFD it will work provided your not silly but it may also blow up because of the extra insulation required.
'Inverter Ready' motors are available but not so cheap. I wouldn't trust a cheap Chinese induction motor.

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