[mmjpotter]

Hi Arvidb

Thanks for the interest shown in my cnc project. My controller is a PC based system which uses the main CPU to perform the PID loop control.

I used 2 standard ISA/PCI slot cards. One is an Analog output card to provide 10 volt drive signals, and the second is a 24bit counter card (quadrature input) which continually tracks and records the encoder position .

A priority interrupt is generated every millisecond this provides the base for real-time operation. The computer constructs a memory model of the required move, which is the distance required at the given speed every millisecond. The interrupt routine compares this position with the actual position recorded by the encoder card. The difference (the following ERROR) is converted by the Anolog card to a voltage between 10 volts and this voltage is PROPORTIONAL to the error.

A tacho is fitted to the rear of the motor and the tacho signal voltage is INTERGRATED with the PROPORTIONAL voltage using a summing amplifier, this helps maintain a constant motor speed under varying loads. Implementing the P & I functions of the PID loop are usually sufficient for basic motion control.

This is a FULL closed loop system and offers very high positional holding torque. I use it to drive different machines with motors that range from 160volts @30amps to
Battery operated motors 24volt@20amps. You can mix motor size and power and even have different encoder resolutions on each axis.

Good Luck Arvidb
Mike