Bridgeport BTC-1 Tool Change Causing Issues

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06 Jan 2023 17:38 - 06 Jan 2023 17:43 #261107 by hunterlong
I have a BTC-1 that uses a pneumatic diaphragm to push down the draw bar and release the tool. There is a metal plate that is moved into a notch on the spindle to hold the z-axis into place when this is occurring.

Here is a video of this operation. You can see the metal plate lock the drawbar from being pushed down.

photos.app.goo.gl/4KPwHBbJJ5TxNU2N6

This has been giving me all kinds of headaches. The spindle has to be in the exact z-position for this to work, and as occurs in the video the metal lock plate often gets stuck.

I also think the z-axis is moving a little even with the lock plate, and this is causing some kind of fault disabling the z-axis.

Any way to prevent the slight movement of the z-axis during this movement from causing some kind of fault?

Also, after the drawbar is pushed down, sometimes you have to move the z-axis up slightly to let the metal lock plate release. Could this be automated?

Here are the z-axis settings from the .ini file.
#******************************************
[AXIS_Z]
MAX_VELOCITY = 1.0
MAX_ACCELERATION = 30.0
MIN_LIMIT = -11
MAX_LIMIT = 0.5

[JOINT_2]
TYPE = LINEAR
HOME = 0.0
FERROR = 0.5
MIN_FERROR = 0.05
MAX_VELOCITY = 1.0
MAX_ACCELERATION = 30.0
P = 45
I = 0
D = 0
FF0 = 0
FF1 = 1
FF2 = 0
BIAS = 0
DEADBAND = 0
MAX_OUTPUT = 0
ENCODER_SCALE = 10152
OUTPUT_SCALE = -10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10
MIN_LIMIT = -11
MAX_LIMIT = 0.5
HOME_OFFSET = 0
HOME_SEARCH_VEL = 5
HOME_LATCH_VEL = 0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = NO
HOME_SEQUENCE=0

Thanks,
-Hunter Long
 
Last edit: 06 Jan 2023 17:43 by hunterlong.

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08 Jan 2023 00:46 #261227 by andypugh

This has been giving me all kinds of headaches. The spindle has to be in the exact z-position for this to work


Getting the Z to the exact position chouldn't be hard on a CNC machine, moving axes to exact positions is the main thing they do.
You might need to make your homing system very accurate, using encoder index if available. Are you using G53 in your tool change routine?

I also think the z-axis is moving a little even with the lock plate, and this is causing some kind of fault disabling the z-axis.


Is it an f-error fault or an amp overload fault? Or something else?

Also, after the drawbar is pushed down, sometimes you have to move the z-axis up slightly to let the metal lock plate release. Could this be automated?


Yes. How are you controlling the tool change sequence at the moment? TOOL_CHANGE_AT_.... in the INI or do you have a tool change routine via remapping?

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09 Jan 2023 23:53 #261392 by hunterlong
I think it is a servo amp overcurrent error. It is a NC400 and the fault light turns on. Is there a way to disable the pid loop for the z axis during tool change so that it isn't trying to fight the drawbar pushing it down 0.05" or so? The afterwords re enable it and have it return to the original position?

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10 Jan 2023 23:59 #261512 by andypugh

I think it is a servo amp overcurrent error. It is a NC400 and the fault light turns on. Is there a way to disable the pid loop for the z axis during tool change so that it isn't trying to fight the drawbar pushing it down 0.05" or so? The afterwords re enable it and have it return to the original position?


Yes. But then you might find that the axis drops. Is there a brake on the servo motor? (or maybe the whole axis can hang on the plate?)

Exactly how you disable the PID would depend on how the tool change is being sequenced.

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11 Jan 2023 16:00 #261586 by hunterlong
Yeah this locking plate keeps the z-axis from moving more than a few hundred thousandths when it is engaged. So no brake needed. Also, with the quill z axis I have it doesn't move under the weight of gravity when the drives are off.

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12 Jan 2023 21:10 #261737 by Todd Zuercher
Maybe you might need to add another step to your tool change sequence. It might work to add a step where the Z moves down after the locking plate is enguaged, just enough to take up the lash in the locking plate. Then when the the release pushes down it won't be fighting the servo. Then after the tool change move the Z back up to the beging position before releasing the locking plate.

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