Tool changing on a multispindle machine

Hello!

I am in the process of retrofitting LinuxCNC on an old 3-Axis woodworking router (using MESA 5125 + 7i77). This router does not incorporate a toolchanger as we know it, but has instead 3 spindle motors, each on a separate vertical pneumatic cylinder. All three motors are connected to the same inverter through 3 contactors so only 1 motor is connected at any time.

All valves and contactors are controlled through a Siemens S5 PLC which I have access to modify the logic as necessary. I have 8 parallel connections from 7i77 to the PLC which can be used to issue instructions in the form of an 8bit word.

The following sequence has to be applied for successful toolchanging:

• Stop Spindle from LinuxCNC
• Issue tool change instruction from LinuxCNC to PLC in the form of an 8bit word
• The PLC can then handle disabling 'Inverter Enable', all pneumatic work required, flip contactors and re-enable 'Inverter Enable'
• A feedback 'PLC Ready' is also available from PLC to the 7i77
• LinuxCNC must then compensate for the new tool in a different position on the moving head

Now I would like to make tool changing as seamless as possible using simple Tx M6 in my g-code programs. Does this sound too far fetched?

Additionally the machine has a series of drills (about 15 of them) all mounted on separate pneumatic cylinders, but I am willing to focus on the 3 main spindles for the time being.

Thanks!