Automatic touch off on X axis

Hi all,

I need to configure my X axis to do the following.

The system is a closed loop mesa 5i23 and 7i33 setup with servo and encoder feedback. The X axis is not a fixed length as the machine feeds material in along the X axis. I have two proximity sensors on the entrance to the machine on the X axis.
I need to push a button (VCP) to start the X axis servo and run at a preset speed. This will feed the material. As the material enters the machine the first proximity is tripped. Now the servo must slow down to another predetermined speed until the second proximity is tripped. Here I have to zero or touch off the X axis for the machine to be setup for cutting.

Any takes on what is the best method to apply here? I was thinking to use ladder logic.

Thanks a lot already.

Hi John,
No it is not a simple setup. You may recall I am still busy with the machine that has XYZA, tool changer, triple encoders on the X axis and whole heap of interlock and safety functions. It has a dual head - plasma and 7.5Kw spindle that is rotated by the A axis. The machine is almost 30m long. It will take a 9m length of all kinds of sections and do drilling, cutting and plasma operations to the whole length of material and then push it out on the other side when done.

I have to load the new piece of metal and start the whole process again. The metal is loaded on a conveyor system further down from the machine and I use the X axis to pull it closer. The X axis is a driven roller conveyor. All the rollers are driven simultaneously by the X axis servo.

The sequence you describe in your first post sounds a lot like a homeing sequence. I wonder if you could just hit home X, then after you have processed that piece of material, "unhome" it and start the process again?

I am pretty sure you can invoke the unhome from a button, or maybe even as the end of your part program? This would also have the added benefit of not needing to "un-wind" so to speak your X axis as you keep going in 1 direction and the "position" just keeps getting bigger.

Yes I agree with the homing idea. It would seem logical. Two questions please.

1: Would you know what signal or pin is activated when the home X button is pushed in Axis?.
I would have to hijack that signal. Then I could set the homing speed high at first and look for the switches in ladder logic to reduce the homing speed.

2: Will it make a difference to EMC if the Home switch stay engaged while cutting. The proximity switch will be activated as long as there is a piece of material on the machine.

BigJohnT wrote:

Yes, I remember some now. On my plasma I Z down using a probe move then using G92 I set the Z offset. This could work in your set up as well I think. I assume once you locate the material you want to use G code to run the machine.

Very interesting challenge...

Actually two probe moves would work I think, one fast to get to the initial prox then one slow to move to the second prox. If you set no force homing then you don't have to worry about soft limits...

John

John I am running Gcode but the material handling must be done outside of the program. All buttons and manual activated functions - mainly for safety and ease of operations as far as the operator goes.

Hi,

mariusl wrote:

Yes I agree with the homing idea. It would seem logical. Two questions please.

1: Would you know what signal or pin is activated when the home X button is pushed in Axis?.
I would have to hijack that signal. Then I could set the homing speed high at first and look for the switches in ladder logic to reduce the homing speed.

2: Will it make a difference to EMC if the Home switch stay engaged while cutting. The proximity switch will be activated as long as there is a piece of material on the machine.

1. The easiest interface to what you need would probably be halui
linuxcnc.org/docs/2.5/html/gui/halui.html

You can do everything Axis does with it

2. If you follow the normal homing route, your second switch (the homing one) will not be activated. It will roll up to and activate the switch and then roll back until it deactivates, then set G53 X to zero.
You could adjust the position of your switch to compensate for any slight difference.

If you are just using the first switch as a trigger to reduce feedrate through CL or a component, it would make no difference if it stays High, until you next want to move the X axis, then you will have to do something to restore the feedrate.

regards

I have the homing cycle working with the second switch through the normal buttons on Axis. Now I have to get the custom button to start the X axis and use the first switch to unhome the X axis as well as reduce the speed