Electric motor actuator

An electric motor actuator comprising:

• an electric motor provided with reduction gear means;
• first encoding means mounted on a rotation shaft of said motor for generating output pulses in accordance with the rotation of said rotation shaft of said motor, said first encoding means generating output pulses of a number PPR.sub.1 for each revolution of said rotation shaft of said motor;
• second encoding means mounted on an output shaft of said reduction gear means for generating output pulses in accordance with the rotation of said output shaft of said reduction gear means, said second encoding means generating output pulses of a number of PPR.sub.2 for each revolution of said output shaft of said reduction gear means;
• and
• means responsive to the output pulses from said first and second encoding means for calculating a difference between the output pulses from said first and second encoding means to thereby detect a torsion corresponding to an erroneous difference in rotation between said rotation shaft of said motor and said output shaft of said reduction gear means;
• wherein the respective numbers PPR.sub.1 and PPR.sub.2 of said output pulses of said first and second encoding means are set to satisfy an expression
• PPR.sub.2 =NPPR.sub.1
• under a condition where no torsion exists in said reduction gear means, N being a reciprocal number of a reduction ratio of said reduction gear means so that said second encoding means provides a number of output pulses greater than the number of output pulses provided by said first encoding means and equal to the number of output pulses provided by said first encoding means times the reciprocal number of the reduction ratio of said reduction gear means.