User project:VMC100 CNC mill update

I have replaced a 80s EMCO TM-02 controller with MACH3 PC based control system including new electronics for a VMC-100 CNC mill.

There is a servo controller, stepper controllers, programmable logic controller (PLC) and some power supplies and minor things. Interface to PC is via parallel port, using a VSDEPI break-out-board (BOB) from Granite devices. The original connectors are cut away and cables are connected to new electronics located in a metal cabinet bolted to the left side of the mill. There is also a large transformer for changing 230Vac voltage to 110Vac for the Vexta stepper controllers - this voltage is also handy for the servo powersupply, and offers isolation from mains.

Servo controller is Granite Devices VSD-E 160. It has a simple 150Vdc high-voltage powersupply based on a rectifier bridge and storage capasitor. PLC controls a relay that short-circuits a current inrush limiting resistor at the DC powersupply circuit. There is a bleeder resistor to bleed the charge from capasitor when power is switched off - the energy stored in the capasitor is easily enough to kill a person. Spindle control is with step-direction -control from PC. The tool changer rotation is based on spindle servo, so spindle had to be a true servo spindle instead of a more simple RPM control. In the servo controller there is scaling of the input pulses so that the full speed of spindle can be reached with the limited pulse rate of PC parallel port. This limits angular accuracy of spindle, but is a necessary compromise.

Stepper controllers are Vexta (Oriental motor) UDK5128. They can drive the 5-phase penta-connected original Berger-Lahr steppers of the mill. The control is with step-direction -control. I have also added X and Y axis limit switches, as EMCO design relied on software limits only. The overheat output signal goes to PLC from stepper controllers, and PLC controls enable input of stepper controllers. The stepper input/output signals are optically isolated so interfacing is simple.

Here is a conceptual schematic:

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