US 5,309,075 AGranted

Digital servo-control apparatus for preventing torque variations

AssigneeToyoda Koki Kabushiki Kaisha

InventorsIsamu Yokoe, Toshio Kohno, Yasunori Masegi

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Abstract

An apparatus for preventing torque variation in a digitally controlled servomotor. Electrical angles .theta..sub.1 and .theta..sub.2 of the exciting magnetic field or the armature coil at respective timings of detecting and controlling a load current are obtained. The current is dq-transformed with .theta..sub.1 and inverse-dq-transformed with .theta..sub.2. As a result, even if there is a displacement of the actual electrical angle owing to the rotation of the armature during computing, it is possible to execute accurate current control. Further, at the time of calibration of the control system, the load currents are detected to be dq-transformed. From the d-axis components and q-axis components, values related to the offset and the amplification factor of the current detection systems are calculated. During the actual operation of the servomotor, the detected current value is corrected using the values. Further, the detection of the load current is performed plural times in one control cycle. Thereupon, a statistical average value is obtained as the detected current. Accordingly, an undesirable variation of the output torque is prevented.

Claims4

Dependent claims

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.

4 more elements

Dependencies are inferred from the claim text.