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Author Topic: Lathe turret design  (Read 6393 times)

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Lathe turret design
« on: April 06, 2012, 08:29:48 PM »
Hello all,

I'm working on retrofitting a Hardinge CHNC. It's running pretty well now, but I'm having troubles with my original solution to turret indexing. I'm using a stepper to index the turret as if it were a rotary axis.  I have one home switch which corresponds with tool 1/0deg. From there its just a matter of indexing to each tool position by degrees.  The turret locks in place via a raise/lower situation.

Unfortunately, it's proven unreliable. There's a lot of backlash in the gear train that drives the turret, and the steps per degree don't work out to an even number causing further frustration.

I'd like to set it up with 8 sensors, one for each position, and I have enough inputs left for them.

So my question is, could this type of setup be easily controlled by a macro? Just run the stepper till it hits the right sensor? I'd rather go this route as I have no experience with PLCs or ModBus.

Thanks for any ideas,

Kevin
Re: Lathe turret design
« Reply #1 on: April 07, 2012, 04:39:39 AM »
I am not sure you need EIGHT sensor inputs. Put a good RC filter on each sensor output and then combine them all together, and bring them in on one pin. (How you combine them depends of what sort of sensors you have.)

Then when you want to index to another tool, watch the input pin. It will start giving an 'active' signal (meaning the turret is at one tool), then it will go inactive while the turret advances to the next tool. When it gets there the pin will go active again. Assuming good filtering so you don't get noise, this should be fairly reliable. It can be done with a macro.

Cheers

Offline RICH

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Re: Lathe turret design
« Reply #2 on: April 07, 2012, 06:10:26 AM »
Suggest you do a search and have a look at what Hood has recently done. My only comment is that you want the turret to lock up tight.

RICH

Offline Hood

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Re: Lathe turret design
« Reply #3 on: April 07, 2012, 10:03:44 AM »
My preferred method would be to have triggers at each position and use multiple switches for each tool, that way it should be impossible for it to be at the wrong tool and at the same time only use 4 switches for the 8 positions.
Hood
Re: Lathe turret design
« Reply #4 on: April 07, 2012, 04:22:49 PM »
Hood, can you suggest a possible arrangement for the switches as you describe them? My plan is to use stationary Hall sensors and a rotating disc with magnets.

Kevin

Offline Hood

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Re: Lathe turret design
« Reply #5 on: April 07, 2012, 04:27:54 PM »
Well for 8 positions you would need 4 switches and they could be something like this
Tool 1 = 0 0 0 1
Tool 2 = 0 0 1 0
Tool 3 = 0 0 1 1
Tool 4 = 0 1 0 0
Tool 5 = 0 1 0 1
Tool 6 = 0 1 1 0
Tool 7 = 0 1 1 1
Tool 8 = 1 0 0 0

Hood
Re: Lathe turret design
« Reply #6 on: April 07, 2012, 04:53:28 PM »
you can do it with three switches.

000
001
010
011
111
110
101
100

Offline Hood

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Re: Lathe turret design
« Reply #7 on: April 07, 2012, 04:58:00 PM »
Not really as when it was in between positions it would think it was at a tool position if you had 0 0 0 as one tool position.
Hood
Re: Lathe turret design
« Reply #8 on: April 07, 2012, 05:17:45 PM »
that's only true if you allow them to go to all zeros between changes

Offline Hood

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Re: Lathe turret design
« Reply #9 on: April 07, 2012, 05:19:46 PM »
How would you not?
Hood