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Ref all axis, and soft limits
« on: February 25, 2014, 08:43:28 AM »
Warning, Blonde questions coming!
Is there a way to enable soft limits on a machine which you have not referenced. Surely with persistent DRO’s enabled, as long as mach3 was shut down correctly, there has been no manual moving of machine then it should be ok??

How acculturate is if the referencing of all axis? If I were to make a jig to bolt to my table to hold a part, and I re referenced my axis,  how close in mm would you expect the jig to be to last time it was referenced?

Thanks

Jim

Offline Fastest1

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Ref all axis, and soft limits
« Reply #1 on: February 25, 2014, 11:23:18 AM »
How many steps per unit are you set up with now?
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)

Offline Hood

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Re: Ref all axis, and soft limits
« Reply #2 on: February 25, 2014, 01:14:22 PM »
Is this with the IP-A?



Hood
Re: Ref all axis, and soft limits
« Reply #3 on: February 25, 2014, 01:26:58 PM »
Yes this is with the ip-a. I'll check the steps per unit

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Re: Ref all axis, and soft limits
« Reply #4 on: February 25, 2014, 01:40:00 PM »
Ok well you have to reference the machine when you first start if you want soft limits with the IP-A as it needs to know where it is so it can set the soft limits. If  you have persistent offsets chosen then you may think it will be the same position when you shut down and restart but I can guarantee it will not be and that has nothing to do with it being the IP-A. It will happen with any system whether servo or stepper. If you want to see you can simply press Reset and watch the DROs in Mach, they will change slightly and again when you take Mach out of Reset again, that is assuming of course you keep the encoders alive and are disabling the power stage of the drives.. The reason is you have forces acting on the axes, whether that be gravity or even just belt tension and as soon as you disable the servo drives they will not be holding position and the axes will move slightly, it may be a small amount but it will move. On a stepper system it will be similar, as soon as the drives are disabled the stepper will jump to the nearest full step of the motor.
 So each time you do that you will be out by a small amount.


Now homing, the IP-A is capable of Index homing, you should use that as it is extremely accurate. What happens is the machine homes to the mechanical switch then reverses, when the switch again closes the axis continues until the Index pulse of the encoder is seen, that iis then your machine homed, it is the way almost every industrial machine homes and as said is extremely accurate.

Hood
Re: Ref all axis, and soft limits
« Reply #5 on: February 25, 2014, 02:30:45 PM »
Thanks for clearing that up hood. After re homing, will the home position be accurate to .005mm? Or is that asking too much?

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Re: Ref all axis, and soft limits
« Reply #6 on: February 25, 2014, 03:05:18 PM »
I would say it should be if you are using the Index Homing. Here is a video of my Chiron showing the Index Homing working. The Haimer has graduations of 0.01mm but when I jog at 0.001mm increments I can see each movement of the needle so I can safely say that I would have noticed on the Haimer if the homing had been out even 0.001mm.

http://www.youtube.com/watch?v=7jpnjLVKZN4

Hood
Re: Ref all axis, and soft limits
« Reply #7 on: February 25, 2014, 03:20:24 PM »
Impressive, would you expect my bridgeport to be as good? Are your home switches anything fancy?

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Re: Ref all axis, and soft limits
« Reply #8 on: February 25, 2014, 03:42:43 PM »
The home switches on the Chiron are good quality Euchner but as long as the switches are fairly decent then it doesnt matter too much as it is the Index pulse that is the final factor in the home position. What I mean is as long as the Index pulse is a sufficient distance away from the switch closing then even a switch that is not exact will work. If your Index pulse was such that it was very close to the mechanical switches closing point and the switch had a variance in its closing point then there is a possibility that you could end up a full revolution out.

Hood

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Re: Ref all axis, and soft limits
« Reply #9 on: February 25, 2014, 03:52:29 PM »
i think you anserd my quesgen when i go for coffey i turn of power to stepper drives i come back turn them on again it must move a bit