US Patent No. 9,448,545

SERVO CONTROL DEVICE FOR PERFORMING CORRECTION BASED ON AMOUNT OF STRETCH OR CONTRACTION OF BALL SCREW


Patent No. 9,448,545
Issue Date September 20, 2016
Title Servo Control Device For Performing Correction Based On Amount Of Stretch Or Contraction Of Ball Screw
Inventorship Yasusuke Iwashita, Yamanashi (JP)
Kenichi Takayama, Yamanashi (JP)
Satoshi Ikai, Yamanashi (JP)
Assignee FANUC CORPORATION, Yamanashi (JP)

Claim of US Patent No. 9,448,545

1. A servo control device for controlling a feed axis which converts rotational motion of a servo motor into linear motion
of a moving body by way of a ball screw,
wherein the ball screw is supported at opposite ends thereof by a first fixed unit arranged at one end of the ball screw closer
to the servo motor, and by a second fixed unit arranged at the other end of the ball screw, respectively,

the servo control device comprising:
a position command generating unit for generating a position command associated with a position of the feed axis;
a torque command generating unit for generating a torque command for the servo motor;
a thermal displacement amount calculating unit for calculating an amount of thermal displacement of the ball screw;
a tension calculating unit for calculating tension acting between the ball screw and the second fixed unit, based on a distance
from the first fixed unit to the second fixed unit, a distance from the first fixed unit to the moving body, the amount of
thermal displacement calculated by the thermal displacement amount calculating unit, and the torque command generated by the
torque command generating unit;

a stretch/contraction amount calculating unit for calculating an amount of locally-generated stretch or contraction of the
ball screw during operation of the servo motor, based on the tension calculated by the tension calculating unit, the distance
from the first fixed unit to the second fixed unit, the distance from the first fixed unit to the moving body, and the torque
command generated by the torque command generating unit; and

a position correction amount calculating unit for calculating an amount of position correction adapted to correct the position
command associated with a position of the feed axis, based on the amount of locally-generated stretch or contraction calculated
by the stretch/contraction amount calculating unit.