a reciprocating drive mechanism , capable of producing a substantially trapezoidal velocity profile , reciprocates the hammer banks of a dot matrix printer , or printers in general , at a relatively high frequency , and a high constant velocity . utilizing a set of non - linear springs , the hammer banks are reciprocated at one of the many possible resonant frequencies of the non - linear spring mass system , thus minimizing power consumption . single action solenoids or a voice coil type motor is servo controlled to compensate for the energy loss due to damping . an optical switch establishes the zero position of the hammer banks at midlength of the travel . a velocity transducer measures the velocities at all positions . by integrating the velocities , the positions at any time of travel is known for proper placement of the print dots .