gear hobbing maschine-electronic gearing ?

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30 Sep 2016 21:02 #81120 by viski
Hello!

I am thinking to upgrade existing mascine from mehanical gearing to electrical but , would be linux CNC able to do that?

How machine works :
Maschine Diferential is 12 . So , if i want to make 18 teeth i have to calculate gears a, b, c, d or a and d. a is master and d is slave.
soo.. 12/18 is 0,666666666667 . That i will get 18 teeth gear a(master) is 40 teeth and gear d ( slave) is 60 teeth .

If master gear rotate at speed 557 rpm , slave must rotate at speed 371,33333333333333333333333333333 rpm .

Could linux cnc controll at this speed and how ?

Maybe mesa card + analog drive +/-10 vdc or pluto p + hbridge + encoder feedback ?

What would you sugest me?

With best regards,

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02 Oct 2016 16:40 #81150 by andypugh

viski wrote: I am thinking to upgrade existing mascine from mehanical gearing to electrical but , would be linux CNC able to do that?


Yes, LinuxCNC can do this very easily. LinuxCNC can do this very easily.

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02 Oct 2016 16:44 #81151 by andypugh
This machine of mine is closer to what you are talking about



There is an encoder on the hob spindle and then the work axis is synchronised to that by a servo motor and its encoder. You can do it with any LinuxCNC-supported hardware, it really is a very simple bit of HAL setup.

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04 Oct 2016 09:57 #81208 by gaston48
Hello,
Also possible to machine a helical gear, with an encoder
coupled to the axis X

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04 Oct 2016 10:11 #81209 by andypugh

gaston48 wrote: Hello,
Also possible to machine a helical gear, with an encoder
coupled to the axis X


Yes, my hobbing setup for the mill allows me to cut helical gears too.

I have a GladeVCP screen that does basic gear calculations and cuts the gears:

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11 Oct 2016 20:40 #81563 by opw
Hi Andy,

Every since seeing your electronic hobbing video I have wanted to setup something similar. As I am exploring Linuxcnc I discovered encoder_ratio component.
On the Linuxcnc wiki you have documented your setup. I was wondering why you did not use the encoder_ratio component for gearing. Is this not suitable for the hobbing setup and realizing an 'electronic gear'?

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11 Oct 2016 21:08 #81564 by andypugh

opw wrote: I was wondering why you did not use the encoder_ratio component for gearing. Is this not suitable for the hobbing setup and realizing an 'electronic gear'?


The emcoder_ratio component needs a quadrature encoder on both axes. It counts the A/B pulses of both encoders in software.

My first setup used a Mesa card to count the spindle revs (so HAL never sees the A/B pulses) and a stepper on the work axes (so no slave pulses) and my current setup uses a resolver on the spindle (so no A/B pulses exist anywhere) though it does have an encoder on the slave.

I rather feel that encoder_ratio solves the problem the hard way, and only in a limited set of circumstances.
The following user(s) said Thank You: opw

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03 Sep 2020 14:36 #180552 by jefsaro

File Attachment:

File Name: tailleuse....09-03.gz
File Size:19 KB


hello andy,
I made this machine with your help, 10 years ago, it works perfectly in straight cutting, I would like to make the helicoidal, but I do not know how to do it, I attach my configuration.
thanks for the help
have a good day
jf
Attachments:

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03 Sep 2020 16:12 #180558 by andypugh
Helical _ought_ to be fairly easy. But I have not tried it yet.

I know that I claimed to have done so above, but I haven't hooked it up yet.
In theory you just need to add some proportion of the absolute X position to the workpiece angle.

I currently use this HAL component:
component hobbing "synchronise a rotary axis to the spindle";

pin in float teeth;
pin in float starts = 1;
pin in float spindle-pos;
pin in float spindle-vel;
pin in float A-pos-cmd;
pin in float gear-pos-fb;

pin out float gear-pos;
pin out float gear-vel;
pin out float A-pos-fb;

author "andypugh";
license "GPL v2+";

function _;

;;

FUNCTION(_){
    static double pos_ref;
    static double spindle_ref;
    static int old_teeth;

    if (old_teeth != teeth){
        pos_ref = gear_pos_fb;
        spindle_ref = spindle_pos;
        old_teeth = teeth;
    }
    if (teeth != 0) {
        gear_pos = pos_ref + 360*starts*(spindle_pos - spindle_ref)/teeth + A_pos_cmd;
        gear_vel = spindle_vel / teeth;
        A_pos_fb = gear_pos_fb - pos_ref - 360*starts*(spindle_pos - spindle_ref)/teeth;
    } else {
        gear_pos = pos_ref + A_pos_cmd;
        gear_vel = 0;
        A_pos_fb = gear_pos_fb - pos_ref;  
    }
}

To cut a helical you would need to add:
pin in float y-pos
pin in float lead

Then in the calculation section:
 gear_pos = pos_ref + 360*starts*(spindle_pos - spindle_ref)/teeth + (lead * y_pos) + A_pos_cmd;

Note that in this example the helix is defined as an angular lead / mm so that the HAL component does not need to know the gear diameter.

In practice I think that I woild have my GUI calculate that, based on helix angle and the gear parameters (because that _does_ know the pitch diameter.
The following user(s) said Thank You: joekline9, CORBETT, jefsaro, Aciera

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