A CNC Block Diagram

This is a block diagram of my CNC system. It shows the CPU, and the Servo-to-Go card that is plugged in to an ISA slot in the motherboard. That card feeds +/- 10 Volt analog velocity signals to the servo amps. It also receives signals from the quadrature encoders on each axis. The servo amps drive the motors, and sense velocity from the DC tachometers reading leadscrew rotational velocity. Each servo amp has a fault relay that opens if the amp has been overloaded or otherwise is no longer following commands from the CPU. These are wired in series, and then in series with the Emergency Stop buttons. If any of these contacts opens, it tells the CPU to E-stop, and also shuts down power to the servo amps, and extracts any energy provided by moving parts of the machine.