5. Motor Control

The stepper motors are driven by micro-stepping bipolar stepper motor drivers that receive their control pulses from a separate pulse generator source. The same motors and drivers were used for all Marks of METS but their source and control of pulse generation differed.

PC Pulse Generation

For Mark 1, I had Initially used the PC’s parallel port and pulse streams generated from within MS Windows directly. This arrangement worked but proved inconsistent because MS Windows is a multi-tasking OS being used in a real time application. My stepper motor driver supplier (RoutoutCNC) suggested using MS Windows to control when pulse streams were needed but to generate the pulse streams externally. The change to external pulse generation resulted in a very consistent system.

PC Control via Serial Port of a PIC controller

With the demise of parallel ports on modern computers for the Mark 3, I adopted the use of the serial port or a USB to serial port converter cable for inter connection and a PIC processor for pulse generation. This simplified my task of learning to write software for the USB interface and avoided all the quirks of the various versions of Windows (98SE, ME, 2000, XP, Vista and now 7), plus the cost and complexity of USB licensing.

The PIC processor kit card used has both serial port and USB interfaces. The programs for the PIC chip were written using the Proton Basic compiler to generate the code. A closed loop protocol was used between the PIC processor and PC.


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