torch height control and limit switches

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14 Dec 2019 21:17 #152662 by stevebowen
ive managed to get LinuxCNC 2.8 installed and working fairly well with RTAI latency of about 11uS
thanks to help from everyone.

I'm getting ready to start wiring and testing steppers and limit switches. I'm not sure how to wire limit switches and how many inputs I need. I have a gantry machine built with two steppers on the Y-axis. Im using inductive proxity sensors that I purchased on Amazon.
8 total front and back on x z axis and on both sides of the y axis front and back on Y1 and Y2.
for the x axis can i combine both sides with diode or gate to have one input to the breakout board. On Y1 and Y2 can I do the same for the front and back for two input to the breakout board? One for front and back on each side? For the Z axis Do I use two switches top and bottom the same? Do I need another input for sensing the metal? Sorry if I'm rambling a bit.

It seems like I need at least 3 inputs for all of these limit switches or maybe more.

Then for torch height control how many inputs do I need?
Is there a frequency input available to LinuxCNC using PlasmaC

Am I gonna have to use two parallel ports for a plasma cutting machine in order to have enough inputs?

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14 Dec 2019 22:01 #152664 by tommylight
Linuxcnc can do all the homing and limits in one single input. It does take a bit to get it right in HAL.
PlasmaC has a frequency input used for THCAD, so you can connect anything else that can provide frequency.
Pins for THC, what THC? Proma 150 and similar require 3 inputs, Proma SD does not require any as it disconnects the step/dir from the computer to the drives and makes it's own pulses while cutting. THCAD requires only an encoder input or a single input to the parallel port for counting.
The following user(s) said Thank You: luizdiefenbach

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15 Dec 2019 02:41 #152669 by stevebowen
Okay thanks much Tommy.

1. The proximity switches I have are 3-wire NPN 6-36V inductive sensors. I assuming the signal out is 6-36 volts so I either need
to run all into one optoisolator or optoisolate each and combine that into one input at the breakout board. I think I can muddle through
that okay. If the hal logic can work for one input then that seems okay too. I was worried about each gantry stepper affecting the homing but i suppose either the software works it out or you have to decide which side is homed first.

2. Looks like the proma SD hijacks the stepper from Linux CNC starts working. Im assuming this is starts with the Arc Okay signal?
And Linux CNC still controls touch off, start height and moves up for tool path motion?

3. What is the difference in PlasmaC and THCAD are these both LinuxCNC 2.8 Hal components? If I use a frequency to represent
arc voltage is this returned to Linux CNC through a parallel port input pin? This would require only one input or another for arc okay?

4. With PlasmaC and THCAD can I completely eliminate the torch height controller if I convert arc voltage to frequency by for example mapping voltage to frequency with an arduino nano etc?

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15 Dec 2019 03:16 #152674 by tommylight
Sorry i missed the gantry part, so that will not work with only one input.
PlasmaC is a Linuxcnc configuration for running plasma cnc machines with everything included.
THCAD is an isolated voltage-to-frequency converter specially made for Linuxcnc and plasma cutters by Mesa in the U.S. by PCW who is a valued member of this forum.
Here are some links, have a read through, plenty of information there.
forum.linuxcnc.org/plasma-laser/35349-op...general-idea?start=0
forum.linuxcnc.org/plasma-laser/34978-th...-with-how-to?start=0
Regards,
Tom.

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15 Dec 2019 04:32 #152676 by stevebowen
On the Z axis home is basically all the way to the top limit is bottom full travel

So can i connect z home and limit, touch off, x axis home and limit and y1 axis home and limit all to one input and y2 home and limit together to a second input
for a total of two inputs?

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07 Jan 2020 19:56 #154244 by andypugh

1. The proximity switches I have are 3-wire NPN 6-36V inductive sensors. I assuming the signal out is 6-36 volts so I either need
to run all into one optoisolator or optoisolate each and combine that into one input at the breakout board.


Actually.... NPN proximity sensors act as a switch-to-0V so can be used directly on a parallel port pin.

It works fine, even if the prox is connected to 36V. I have done it on a machine that ran for years. It feels risky, though.

black to parallel port pin.
blue to p-port gnd, pc gnd and power supply gnd.
brown to prox power supply. I would suggest that 6V is a wiser choice than 36V in this case.

Because the sensors act as a switch-to-gnd it is easy to wire them in parallel to give an electrical "OR" function, so with suitable INI and HAL setup the sensors for each axis (and each end of each axis) can easily share a single p-port pin.

But, to get proper gantry homing you need two to work independently, so you could use one input for X and Y1 and the other for Z and Y2, for example.

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11 Jan 2020 00:18 #154591 by stevebowen
Thanks much. I had imagined i might need diodes at each input but maybe not.
And I had thought I would need three inputs didn't cross my mind to an x and z with each Y.

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