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Digital servo-control apparatus for preventing torque variations

  • US 5,309,075 A
  • Filed: 03/22/1991
  • Issued: 05/03/1994
  • Est. Priority Date: 03/23/1990
  • Status: Expired due to Fees
First Claim
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1. A digital servo-control apparatus having a current feedback loop for sampling a load current to an AC servomotor of three-phase type at a predetermined control interval thereby obtaining a current feedback value and digitally controlling said load current according to said current feedback value and a target value of said load current, wherein said digital servo-control apparatus comprises:

  • current detection means for detecting, as said load current, load currents of at least two phases;

    amplifiers for amplifying output values of said current detection means;

    detected current transformation means for obtaining as said feedback value, from output values of said amplifiers, a d-axis component representing a reactive current component and a q-axis component representing an active current component in a dq-coordinate system;

    parameter calculation means for sampling, during calibration of said servo-control apparatus, said output values of said amplifiers at a plurality of points of time during a predetermined period and determining, according to time-dependent characteristics of said d-axis component and said q-axis component obtained by said detected current transformation means, parameters related to amplification factors and offset values of current detection systems formed of said current detection means and said amplifiers; and

    correction means for correcting, according to said parameters calculated by said parameter calculation means, said output values of said amplifiers on a real-time basis while said servo-control apparatus is being driven during normal operation,wherein said parameters are determined so that fluctuations of said d-axis component and q-axis component are eliminated.

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