Defining the I/O for the Acorn system

Much of the schematic is fairly obvious but there are a few areas to think about carefully that are yet to be defined. Here's my current thinking:

Power circuits:

It's looking like this:

• PC always powered up when the system is plugged in. That way I can use it for CAM etc without having to power up the main system.
• Main isolator on front panel powers up the transformer, VFD, power supplies, Acorn etc when turned on.
• e-stop circuit isolates the power to the servo drives (by cutting the mains supply to the transformer), coolant pump, power drawbar and VFD - and inhibits the drives and the Acorn. It has a set of aux contacts as well as power contacts, so should be enough to go round.
• I have a couple of DC SSRs for controlling the spindle gears (if I have enough outputs left over) and a couple of AC SSRs for the coolant pump

In terms of "PLC" inputs and outputs, the Acorn is fairly limited. There are 8 of each:

Inputs:

• Home switches(x3 - "simple" scheme)
• Drives OK
• Probe x2
• External e-stop button / hard limits.
• Handwheel?? How does that work?

Outputs:

• e-stop contactor drive
• VFD direction
• VFD enable
• Spindle speed range
• Coolant pump

Other I/O:

• Spindle encoder (I will need a converter to generate the required complementary signals from my Hall effect sensors).
• Spindle speed control (0-10V).
• 4 channels of step, direction, 

External connections:

• 4th axis connector
• Ethernet connection for PC
• Power cable for PC (19V - the power brick will be in the cabinet)
• Servo cables (DC and encoder for each axis)
• Limit switches (X&Y - from knee)
• Limit switches (Z) - come in through different conduit.
• Spindle encoder (converter required?)
• Gear range selector (24VDC to each solenoid from SSRs)
• Power drawbar enable signal (ie 12V "spindle stopped" signal from VFD)
• MPG pendant??? Not sure how / if this can work. Can I use a USB version?
• Coolant pump drive (240V from SSR)
• Lube pump supply (240V continuous)

Panel switches, sockets etc:

• Main power isolator
• "Remote digital operator" panel for VFD
• Main power input socket
• Cabinet cooling fan