cnc winder controller board

[-Elepro-]

after gaussmeter project i'm starting to project a board to control a 2 stepper motors cnc winder....

at this moment i thought to control:

turns
pitch (with 0.0025mm resolution)
speed
acceleration at start
deceleration at end
emergency stop (immediate)
pause (stop with deceleration and resume with acceleration)

any suggestions for other control?

bye

[defaced]

pitch (with 0.0025mm resolution)

Just for a sanity check, is that a realistic number? That's 0.0001", which is the kind of tolerance that's usually reserved to things like interference fit parts and tools. I'm far from a CNC expert, is seems to me like it'll be difficult to achieve/verify and unnecessarily fine for the application. Wouldn't something more reasonable, like 0.005" (0.127mm), suffice?

[-Elepro-]

hi Mike,

naturally 0.0025 is "electronic resolution" and does not take care of backlash leadscrew

but...

this board will control 200step/rev motor in half-step mode then you wil have 400 step per revolution....
traverse will be moved by 1mm pitch leadscrew... (1mm/400step=0.0025mm per step)

if you set control board to have 0.0025mm pitch, you will have 1 step for traverse motor every complete revolution (400 step) of other motor

bye

[defaced]

That makes sense, thanks for the explanation.

[-Elepro-]

for speed regulation i thought 200 - 2000 rpm in 10 step....

what about this?

[-Elepro-]

first 500 turns test..... ok ok there's some vibrations

video

[David King]

Elepro,
that looks promising, how many mice do you have in that box to make it turn so quickly?. I'm interested. My new winder will have a 3 phase industrial motor connected to a programmable Variable frequency drive. (Older Reliance 500 drive off ebay). Will such a PIC be able to send instructions to any VFD or do I need the latest?
Also: What about variable turns per layer to replicate hand wound coils?
What about some tension control so as to slack off wire tension from start to finish? Or at least a simple feedback loop for tensioner..

[David King]

In thinking about this some more I remember that my VFD already has all the speed ramp-up, ramp-down settings adjustable internally. I guess I'd just need a simple switch from the pic to turn the motor on and then use the turns counter to turn it off and let the pic use that as a turns speed indicator to control the traverse accordingly.

Tensioner might need a separate controller?

[-Elepro-]

at this moment the winder has a small steper motor and its max speed is about 600 rpm.... i will change it with a bigger one to have 2000 rpm....
stepper motor are not fast then i will use 2/1 pulley (controller wil have menu for setting 1/1 or 2/1 transmission)

about vfd... it's too different from stepper driver.... steper driver needs two signal: dir (directions 1 or 0) and clock (impulse train... one for each step) then it does not need counter (with shaft sensor) because impulse sent to driver are already exactly.... vfd should have a 0-10 volt in.... but i'm not expert... and i have several stepper motor and driver and not a vfd

Also: What about variable turns per layer to replicate hand wound coils?
What about some tension control so as to slack off wire tension from start to finish? Or at least a simple feedback loop for tensioner..

variable turns per layer could be a good idea... random values around the set value??
at this moment my tensioner is this with rubber inside and a bolt with spring for adjustment.... do you have some idea for controlled tensioner?

[chevalij]

The only thing I can think of for electronic tensioning would be a load cell. But.. you'd have to run the output into a DAQ or similar. Then you'd have to have a small linear actuator or stepper that would apply the pressure. I think with a PID loop you could control the pressure pretty well. By no means cheap... I don't know if they make magnetic brakes small enough ?

[David Schwab]

Also: What about variable turns per layer to replicate hand wound coils?

I think if you don't synch up the traverse with the coil winder you should get a more random pattern.

I'm working on a lathe based winder. I thought about having the traverse run from the main motor, but if I use a separate variable speed motor for the traverse it could be set to be more random, depending on the speed of the two.

At least that's what I was thinking.... but I didn't put a lot of thought into it yet.

This CNC winder looks really cool!

[-Elepro-]

for the time being, i forget controlled tensioner.... electronic is not too complicate but assembly of mechanism, sensor and actuator ... it is .... and i have not a good idea for it....

this is my traverse (and tensioner) now....

I think if you don't synch up the traverse with the coil winder you should get a more random pattern.

yes, this is the problem in winder with vfd for coil motor... you should have a sensor on shaft to control traverse motor in synch... and this is needlessly complicate....

in my project coil motor and traverse motor are perfectly in synch.... watch video and notice that traverse speed is proporzionate to main motor speed...

then, how would you have traverse control?

- adjustable fixed pitch
- adjustable 2 (or x) alternate fixed pitch per layer
- random value around (how many?) the adjustable fixed pitch
- all this

is my english understandable?

[David King]

The only thing I can think of for electronic tensioning would be a load cell. But.. you'd have to run the output into a DAQ or similar. Then you'd have to have a small linear actuator or stepper that would apply the pressure. I think with a PID loop you could control the pressure pretty well. By no means cheap... I don't know if they make magnetic brakes small enough ?

Well from looking at some of the existing tensioners, they fall into a couple of categories. Older types use friction pads with wool felt pressing on both sides of the wire. A solenoid or a piezo actuator could press the felt tighter on the wire as the volts /amps increases.
The newer type have moving parts where the wire wraps a full turn around a wheel or pulley that's connected to a small DC generator/motor. Depending on the resistive load across the motor you can vary the tension on the wire with a good deal of accuracy.

[salvarsan]

The only thing I can think of for electronic tensioning would be a load cell. But.. you'd have to run the output into a DAQ or similar. Then you'd have to have a small linear actuator or stepper that would apply the pressure. I think with a PID loop you could control the pressure pretty well. By no means cheap... I don't know if they make magnetic brakes small enough ?

If you put a felt tensioner one to two feet from the coil, you distribute
the wire stretch better at higher wind rates.
It is simple, inexpensive and easily tunable.


To get an idea of the engineering for an electronic tensioner,
run the numbers for a 5" coil circumference at 1200rpm (20 Hz).

The wire tension has a maximum tension as the bobbin ends pass
through Top Dead Center (TDC).

Estimate that there is a 1 inch section of wire under stress for that
period which is roughly 1/8 of a revolution and occurring twice each
revolution. One revolution takes 50milliseconds and the TDC event
lasts 6.25ms.

At the very least, you need to sample the wire tension sensor every
3.125ms (=320 Hz) and have a servo that adjusts in even less time.
Personally, I'd sample at 10x the event frequency (if possible) or 1600Hz.

FWIW, resistance strain sensors in the 0-100 gram range cost about
$120 the last time I looked.

-drh

[David King]

Interesting. It never occurred to me to try vary the tension mid-turn in time with the rotation but since we know precisely where the coil ends are at all times via the stepper motor, it would be possible to alter the tension without sampling it at all.

I don't see the point of that since tension from a friction pad is going to be constant regardless of the speed that the wire is being pulled through the felt pads (provided it's always moving and not subject to the initial friction which is higher.)

It would be more to the point to take up the slack with a low inertia "dancer" (with our new-found magnetic damping of course.)

I was just wanting too slowly decrease friction during the wind in a linear fashion from start to finish. I'm not sure if that is even useful.