I see the need for four limit switches. Two on each side of the machine along the centerline of the grinder. Label them Left far, Left edge, Right edge, and Right far. Left and Right edge tells you the plate has cleared the grinder.
Left far PLUS Left edge tells you the plate is off the grinder to the left.
Right edge PLUS Right far tells you the plate is off the grinder to the right.
LF & LE & NOT (RE) = Start belt feed to the Right
RF & RE & NOT (LE) = Start belt feed to the Left
LE & RE = Plate in grinder, direction UNKNOWN
You also need manual belt drive controls to load the plate in the grinder, E-stops for operator safety. some sort of counter or limit switch when the plate is done. You will need to set the slew rate and time when reversing the belt direction. Also auto/manual selector, possibly a status light to tell you what mode it is in. How do you set the grinding height.
This sounds like a small PLC would help with the run logic.
Left far AND NOT
Left edge tells you the plate is off the grinder to the left. NOT
Right edge AND
Right far tells you the plate is off the grinder to the right.
LF AND NOT
NOT RE = Start belt feed to the Right
RF AND NOT
NOT (LE) = Start belt feed to the Left
RE = Plate in grinder, direction UNKNOWN ASSUMPTIONS
1) Limit switch is made only when the plate is actuating switch.
2) This logic only auto reverses the belt drive. It does not contain START or STOP functions. Those need to be added seperately.