Independant multiple Z axes

Hello Everyone

This is my first post here I hope its in he right place please correct me if I'm wrong.

I am building a CNC cutter much like a Zund which will have multiple Z axes which are removable. There will be 3 positions on the machine where you can plug in a Z axis unit. The unit could be a spindle a drag knife , a tangential knife or creasing wheel etc.

I have figured out how to do slave axes (the machine has two motors on the y axis). In the case of the Z axes what I would like is that when an axis is plugged in the axis will automatically home when the plug door is closed (interlock). The axes would be selected by tool number (1-9 position 1, 10-19 position two and 20-29 position 3) the tool offsets would be taken care of by the tool table entries.
ie M6T2 would automatically select the first z axis and move to position without re homing

I have figured out how to connect two 7I76 cards to get enough I/O for the 9 motors and loads of digitals needed for the plug and door interlocks etc

I know that multiple joints can be specified in the INI file for a particular axis and a bit of classic ladder can be used to enable or disable a pid block or step gen but I cannot figure out how the currently selected joint position feeds back to the axis.

I could experiment for hours with his but I thought I would ask to see if the is a simple explanation.

Thanks to everyone in advance

Chris

Hi

Thanks for getting back to me.

There was a typo in my oringinal text I have two 7i76E cards on the same ethernet port with a fast swich and it seems to work well. I also have some 7i85 cards to handle encoder feedbacks, and extra digital I/O if I need it. So no problems with I/O.

The reasoning behind having multiple Z axes is that all offests could be handled in the tool table (can you do this with U,V and W ?) and as you say the gcode would always use Z. I would be interested to know what method you would use to acheive this. Also I am writing a python script that takes a normal Gcode file and add the C axis moves to drive the tangenital knife / creasing modules and I would like to keep it to Z if at all possible.

Currently I am thinking of using classsic ladder to swap the signals to the joint and pid blocks around so that the two unused Z axes hold position at the tool change location. This would mean a lot of signal swapping, when you consider I would have to do the same for the three C axes as well, and it dosen't seem like a very elegant way of doing it.

So basically classic ladder would handle the signal swiching in real time and a python script would handle the initial homing and any Z module changeovers in user space.

Again thanks for the reply

Chris

IF your three Z axis stepper drivers are the same why not route the step and direction wires in the remap to the correct driver, rehome, apply the offset and off you go. I would probably wire in the three homes together and same with limits.

When tool 1-9 is the selected_tool then swap the step and direction wires via relays to the correct z driver.
I have a Biesse 346 with three spindles and the signals going to the spindle get redirected via relays depending on which tool is selected in the TxM6. I did it in python. Instead of rerouting spindle wiring you can reroute the step and direction signals. This assumes you only want one Z working at a time.

I have three spindles with one VFD. So if tool X from 1-10 is selected, I drop Spindle 1 and reroute vfd wires to spindle 1 and so on for the other two spindles. I also have a drill bank of 32 drills, I drop the tools when request via TxM6 and use the offsets in the tool table for all the tools.

Just a thought.

/EDIT: I just reread your post. You are swapping the Z out for a different Z module or all three Z's are on the gantry at all times?
If your swapping out the Z modules then this approach may not apply.

OK so you are swapping out the Z modules. So it would be like a manual tool change. TXM6 in the remap, wait for input, then change Z module press a button, then it will reoute the step dir signals to the drivers then apply the offsets.

just rambling now........

andypugh wrote:

Chris1024 wrote:

There was a typo in my oringinal text I have two 7i76E cards on the same ethernet port with a fast swich and it seems to work well.

It would probably be more reliable to have one 7i76E and then connect a 7i76-not-E to one of the expansion ports. That way there is only one ethernet packet per servo period, no switch is needed and net data flow through the port is reduced.

The reasoning behind having multiple Z axes is that all offests could be handled in the tool table (can you do this with U,V and W ?) and as you say the gcode would always use Z.

You can have UVW offsets in the tool table, but they apply to moves in U, V, W not in Z.

You can probably just run a single stepgen for all Z motors, and enable / disable the drives themselves so that only one moves.
It is probably safer, though, to run independent stepgens and keep the drives powered up and locked.

You might want to experiment with configuring the Z as a gantry, as that solves any homing issues (loadrt trivkins coordinates=xxyzzz)
Then each Z would be a separate joint, and they would home independently but all follow the Z command.

The unusual thing here is that you would disable (in HAL) the stepgen of all but the axes that you want to actually move.

For this to work you would need to do something with the stepgen feedback, either just short-circuit it, or make the F-error limits very large.

You would also need to configure to only allow tool changes at Z=0

Not a good idea pluuging stepper motors while drivers are on. I dont know if it matters if they are enabled or not.

Wow thanks for all your replys!

I am using panasonic a5 servo drives for all the axes and they have high resolution encoders. This means that the step gens have to drive in the MHz region (using the differential outputs on the 7i76E) so I think swapping the electrical signals with a relay would be problematic.

I have tried to disable the step gens on the unused joints but it leads to a follwing error as the joint is still connected to the axis and is expecting to follow the Z commanded position (hence signal switching). I was wondering if there is a way to disassociate the joints from the axis and connect them only when required? I dont see a pin on the joint component that allows this, I don't actually understand how the axis is connected to the joint, I have assumed it is done internally from where the joint apears in the ini file.

Chris