Tree J425 tuning

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17 May 2020 15:16 #168072 by Thods1222
Tree J425 tuning was created by Thods1222
Hello, I have a Tree J425 that I have been banging my head against the wall for some time trying to tune the PID loop. I went through the steps provided by tommylight to accomplish the tuning. Once I figured I had it right I put my dial indicator on an axis and found that the commanded position vs the actual movement was off .003in on a .1" movement. Through continued tweaking of the PID and the FFn values I was able to get it down to .0015 but nothing further. Part of me thinks the hardware is to blame but part of me thinks I am pooching the tune. Any help is appreciated.

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18 May 2020 11:24 #168138 by bbsr_5a
Replied by bbsr_5a on topic Tree J425 tuning
Hi
Welcome
some more infos needed as you may have retrofited the system to a SERVO one
what are the Encoders
there are 2 ways as the Machine itself are deliverd in more then one version
you are facing the problem of the Leadscrew mount not in exact pos and fot fixed on one side only tight to the motor oposit side
Fixed and free run Bearing called

Please Tell what system you got running and maybe the controller type you are dealing

The best way to get this system to a real accurate CNC is to use the Liniar Scale direct Axis mount Glass scales for setprice at 250USD
with 10uM Scale steps that can b devided by 4 signals into the Controller

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19 May 2020 15:22 #168276 by OT-CNC
Replied by OT-CNC on topic Tree J425 tuning

actual movement was off .003in on a .1" movement


How much error are you getting on longer moves? As an example, if you came up .030 short at 1" move, it would suggest you have your encoder scale wrong. If the error is consistent when moving in the same direction, as an example, indicator overshoots by .0015" then creeps back to zero, that is more likely PID tuning. If you're testing in different directions, backlash comes into play. I'm guessing here, your machine has the encoders fitted on the end of the ball screw? Any play in the gib, ballscrew mount, and screw will be masked. I would also check how much lost motion you have during axis reversal. As an example, you're encoder may be counting .003" of movement before the table moves.

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