Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Jimster on February 25, 2014, 08:43:28 AM
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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
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How many steps per unit are you set up with now?
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Is this with the IP-A?
Hood
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Yes this is with the ip-a. I'll check the steps per unit
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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
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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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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
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Impressive, would you expect my bridgeport to be as good? Are your home switches anything fancy?
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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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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
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thanks for the info guys, everyday is a school day!
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thanks for the info guys, everyday is a school day!
So are we sitting in the front with the nerds and thick glasses or in the back with the cool people? I am starting to think the nerds were having fun all along! I wear contacts now so I can look cool. I had great eyes in school. Guess where I sat then?
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I don't mind where I sit as long as I can see the hot girl ;D
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Where is the like button when you need it?
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I did some more reading today, as i just found out cs labs have released an english manual for the ip/a. Previously I had not enabled index homing. I assume with this enabled i will get much moe accurate homing???
this works fine on my Y&Z axis, but when i try to enable this fo the x axis, i get an error when homing that machine
"index distance not allowed in range..."
waht is odd though is that the x and y encoders are the same with 1250 pulses per revolution, so why should one work but not the other??
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Could be your index is very close to your switch closing and thus it is not being seen until the next revolution. If you can just remove the belt and turn the motor 180 degrees and then engage the belt again and see if that helps.
Hood
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Thaks hood,
I've solved this issue now, I moved my home switch slightly along it's axis, i guess it was not in nd ideal place for the encoder.
So hopefully now I should have mouch more accurate homing??
Would I be correct in assuming that havig a higher speed for homing the mahcine will not make it any less accurate at homing?
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Ok moving the switch did the same job as rotating the motor :)
Yes your homing will be much more accurate than using the switch alone, it should be extremely accurate now :)
The speed of homing should not really make too much of a difference in accuracy with the Index Homing.
Hood
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This is working really well now, thanks again for the info
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Not a problem :)
Hood