A scanning head 7, wherein each of the three electric motors is connected with its own negative resistor, each resistor having a resistance value that is adjustable independent of the other two negative resistors, by {HEAD ~ means} of hardware or {TAIL ~ software} 
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A scanning head 7 , wherein each of the three electric motors is connected with its own negative resistor , each resistor having a resistance value that is adjustable independent of the other two negative resistors , by { HEAD ~ means } of hardware or { TAIL ~ software }
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