Ursviken Pullmax Optima 130 press brake retrofit with 4 axis backgage

I am working on an Ursviken press brake retrofit to LinuxCNC and decided to document my progress etc here, and probably ask questions along the way. If you have any hints or advice for me, feel free to say so.

This press brake came with a Compaq pc booting some form of MSDOS and a Mitsubishi FX-64M PLC. The press brake had been forgotten in a warehouse for who knows how long until the current owner ended up buying it. After installation in the shop, upon first power-up, it complained of a depleted PLC battery. Sadly, the new battery didn't recover the lost memory. After multiple unsuccessful attempts to get Ursviken to get the thing working again, they showed me this project. I said I think I can make it run on LinuxCNC.

I pulled the PC and the PLC and installed a "Fanless industrial mini-pc" with 4 ethernet ports. For i/o I am using Mesa 7i80HDT + 7i36 + 7i54 and Beckhoff ethercat EL1409 16-inputs and EL2409 16-outputs.

Original 10 axis configuration was:
Y1 and Y2 = left and right ram (top die height)
X = backgage forward/backward motion
R = backgage up/down motion
Z1 and Z2 = independent left/right motion of the two backgage fingers.
Crowning: This feature currently has a mechanical malfunction so the customer asked me if I could leave crowning as an option for later if he decides he wants it. I said yes.
VDT = variable width bottom die, appears to have been present on the machine at some point but was apparently deleted.
PSB and PSA = automatic sheet lifter with a height axis and an angular axis. My customer requested to remove that because it will be in his way more than he uses it.

Target configuration:
Y1, Y2, X, R, Z1, Z2, and optional crowning. Y2 is slave of Y1. Z1 and Z2 are independent, except they run on the same rail and must not collide.

I see this machine has tonnage control, but I do not find any electronic pressure feedback sensor on the hydraulic system. It does have two servo valves, one for each side, plus an electronic proportional valve for the entire hydraulics. The servo valves appear to pertain to motion speed for each side. I wonder if the proportional valve sets the tonnage? It might get interesting driving that proportional valve with a DC servo motor output. I plan to limit it to one polarity only and try to modulate it to about 50hz PWM. I think it might work to use a software pwmgen running at 50HZ in hal to set the hardware pwmgen to either 0% or whatever pwm % is the max mA rating of the valve coil.

X and R axis each have a Baldor 90VDC servo with tachometer feedback to the Cybelec servo amps and encoder feedback to the PC controller. The Cybelecs' drive power is set with +/-10VDC from the 7i36 card.

I will try to power the servo valves and the proportional valve using the DC servo outputs from the 7i54 card.

Z1 and Z2 axis are DC worm drive motors powered by fwd/rev contactors and basic encoder feedback to the PC.

Crowning is a common AC 3 phase induction motor on a worm gear box driving an ACME lead screw protruding from the left side of the bottom bed. It is powered by a fwd/rev contactor.