Retrofiting an old big milling machine

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12 Sep 2018 19:47 - 12 Sep 2018 19:47 #117426 by vre
The scale is glass because i saw the glass inside.
I found the VCC & GND from TL084CN 4&11 pins.
TL084CN has populated 1&7&8pin but not 14pin.
Are these 3 outputs the U1 U2 U3 ?
The remaining one wire is the 7.5V ?
That is the usage of 7.5V ?
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Last edit: 12 Sep 2018 19:47 by vre.

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12 Sep 2018 21:12 #117430 by tommylight
The TL084 is an operational amplifier so it needs a positive and a negative power supply voltage and a common ground for both of them, so it needs a + and a - 7.5V measured from it's ground in your case.
That looks to be derived from 15V supply in your case.
It can be done simply by using 2 capacitors to quite complicated voltage regulators.

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12 Sep 2018 22:14 - 12 Sep 2018 22:17 #117433 by vre
The schematic shows +15V 0V GND +7.5V
If understand correct the +15V is the +VCC the 0V is the -VCC and the 7.5V is the GND(but the TL084CN has no GND only +-VCC) right ?
I have a symmetric linear power supply +-15VDC/1A but i think the is not suitable for this case...
I need a symmetric +-7.5VDC right ?
What max current is good for powering 3 scales ?
Last edit: 12 Sep 2018 22:17 by vre.

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13 Sep 2018 05:04 #117446 by tommylight
Just a guess but they should not use more than 50mA or 0.05A. They rarely use more.

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26 Feb 2019 15:19 #127164 by vre
I got new scales that output TTL quadrature waveform so now i have 3 scales 3 electromagnets (each electromagnet engages its own axis X/Y/Z)
and one brush DC motor >2kw that moves all axes(engaging correct gears by 3 electromagnets).
The axis will be moved is the axis which its electromagnet is actuated.
The dc motor driven by a big full bridge that accepts direction&pwm signal.
So how to tune the pid in linuxcnc ?
Is there a guide pid tuning for brush dc motor with full bridge and linear encoder feedback ?
I have a mesa 7i80hd .

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26 Feb 2019 15:37 #127166 by PCW
Tuning a Hbridge driven motor (voltage mode) is quite similar to tuning a velocity mode servo where velocity feed forward (FF1) is set to compensate for the motors BEMF

The difference is that unlike a velocity mode servo, voltage mode will likely require substantial D term to remain stable with reasonable P values.
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