Steering Mechanism? how?

hey all the pro's engineer out there, i am a degree student doing a final project. My group is doing the whole AGV for a FMS. The automated guided vehicle is a line following vehicle, and i am in charge of doing the Front wheel steering part. Since it is automatic, we hope th steering system can be as simple as possible.
we plan to use a step motors to control the angle. But we only know how to use PLC to control the motor.
Pls give us some idea and suggestion on the steering mechanism ( plus the design pic) and motor suitable to be use to control by PLC....

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