AcornSix Lathe - C-Axis Configuration

[RC-Lights]

hi guys,

since my lathe is running now very good and stable i want to go the next step and implement the C-Axis with Live Tooling.

i use a 3,7KW Spindle Servo, which supports switching from speed to position mode

i wired it like this:
https://www.centroidcnc.com/dealersuppo ... 220.r1.pdf

after it i used setup the axis in the wizard and used the standard M51 function.

axis was enabled, moving and also find the homing position. so far so good.

but i realised, that 1 rotation of the chuck was not the same like one rotation at the DRO.

so i checked the axis config.

Pulse per REV: i guess 10000. i have no parameters available in the servo drive to adjust the steps, but the encoder is named with 2500E, so i guessed that the pulses are 10000 per rev.

ratio: this is the big question. default was 5mm, the rotation was nearly fine. but i want to calculate it correct.

the servo is connected with two pulleys, first one on servo side is 75mm, second one on spindle side is 120mm. so the gear ratio is 0,625:1

but the wizzard asks for degree per rotation. so one rotation of spindle is 225deg of spindle. i typed 225 in the wizard and tried again, but now the spindle is nearly not moving.

where is my mistake ?

this is the basic question.

second question is:
whats about homing ? do i need to implement the homing of C-Axis to my homing sequence at the beginning ? it is possible that i often have to switch between c-axis and turning with spindle.

third question:
how do i make sure, that the spindle is not turning any more ? the spindle servo has an output for that. or is it enough to wait maybe 2 sec after M5 ?

thank you in advance
Michael

[suntravel]

You have to switch the spindle servo to position mode for C-axis and the servo must be setup to the same Step/Rev like Acorn

The spindle encoder Z index is only used to find C 0 if M51 is issued, no need to home it while starting, but I have this in cnct.hom:

M3 S100
G4P1
M5

to make sure the CNC knows where the index is right after starting.

The default M51 macro is taking care of the spindle speed before turning on the C-axis. As long as M51 is active no way to turn on the spindle.

Uwe

[RC-Lights]

hi Uwe,

thanks. The Servo is switching to Position Mode when activating M51. i see the centroid output activ and the servo become rigid. so this seems to be successful.

this is the manual i have from the servo, no parameter to configure puls per rev or something like that:
http://gofile.me/5RlbJ/f3I2ltyN0

Michael

[suntravel]

I have never bought a servo with <150 pages manual

I think the English version you got is not complete.

Contact the manufacturer, or play with pulse/rev in Acorn till 360deg is one turn.

Uwe

[Chaz]

Almost all of these generic AC servos use 10000 pulses per rev, so that's a good place to start your calcs from.

[RC-Lights]

hi

now i found a complete manual with around 150 pages - but no new information regarding the pulses. the solution was quite easy. i tried 0,625 in the "deg/rev" box and this works quite well. no idea, why i didn´t tried it yesterday.

controlling the axis is also fine, first test programm was successfull - next tasks are to find good parameters for high stiffness and finish the live tooling spindle.

thanks and best regards
Michael

[RC-Lights]

but an additional question - where is the encoder feedback here ? the encoder should realising, that the rotation of the control and the rotation of spindle are not fitting together and give an error message or correct the position / speed, etc.

and the spindle servo isn´t very rigid right now, good parameters are missing. but i can rotate the spindle by some degree i guess. why isn´t the controler trying to correct this missmatch ?

any ideas ?

[suntravel]

For C-axis closed loop you have to use the servo encoder or a second one on the spindle connected to acorn six.

Uwe

[RC-Lights]

Hi Uwe, are you serious?

Why do i need a second encoder, which does exactly the same than the first one? I didn't know that. Encoder on servo does not help me, i want to correct the V-Belt errors with it.

Is there a possibility for a Software solution or are there splitters for the encoders available?

Michael

[suntravel]

I must admit I have not tried to use the same encoder port for the spindle and the C axis.

On industrial machines encoder with min. 9000 lines are used for the C-axis for a fine resolution.
Usually, they have also a second fast low-resolution encoder for spindle use

On my lathe the C-axis is with 4.5 : 1 reduction and 8000 Steps on the drive = 36000 possible steps for the C-axis
So, if I do not want to loose resolution, I have to use a 9000 line encoder for closed loop on the spindle.

Uwe