Servo controller having function for correcting amount of expansion/contraction of ball screw

• US 8,896,255 B2
• Filed: 06/03/2013
• Issued: 11/25/2014
• Est. Priority Date: 06/04/2012
• Status: Active Grant

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Corporation
• Inventors: Iwashita, Yasusuke, Takayama, Kenichi, Ikai, Satoshi
• Primary Examiner(s): Leykin, Rita
• Application Number:
  US13/908,567
• Publication Number:
  US 20130320908A1
• Time in Patent Office: 540 Days
• Field of Search: 318/560, 318/561, 318/567, 318/280, 700/13, 700/12, 700/28, 700/33, 700/45
• US Class Current: 318/632
• CPC Class Codes: G05B 11/011 details of the correcting means
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/41127 Compensation for temperature variations of servo
• CPC Class Codes: G05B 2219/41164 How to compensate, for example by injecting compensation signal in comparator of normal loop

Abstract

A servo controller, capable of controlling the motion of a movable body with high accuracy, without depending on the position of the movable body which is moved on a ball screw. The servo controller has a position command generating part which generates a position command value; a velocity command generating part which generates a velocity command value based on the position command value and a position detection value; a torque command generating part which generates a torque command value based on the velocity command value and a velocity detection value; and a position compensation calculating part which calculates an amount of expansion/contraction of the ball screw based on a distance from the servomotor to a nut threadably engaged with the ball screw and the torque command value, and calculates a position compensation based on the amount of expansion/contraction.

Claims

1. A servo controller for controlling a feed shaft of a machine tool by using a servomotor connected to a ball screw, the servo controller comprising:

a position command generating part which generates a position command value for the feed shaft;

a position detecting part which detects an angular position of the servomotor;

a velocity command generating part which generates a velocity command value for the servomotor based on the position command value generated by the position command generating part and a position detection value detected by the position detecting part;

a velocity detecting part which detects a velocity of the servomotor;

a torque command generating part which degenerates a torque command value for the servomotor based on the velocity command value generated by the velocity command generating part and a velocity detection value detected by the velocity detecting part; and

an amount of position correction calculating part which calculates an amount of position correction for a movable body threadably engaged with the ball screw based on an amount of expansion/contraction of the ball screw, the amount of position correction being used to correct the position command value,

wherein the amount of position correction calculating part calculates the amount of expansion/contraction of the ball screw based on a distance from the servomotor to the movable body and the torque command value generated by the torque command generating part, and calculates the amount of position correction based on the calculated amount of expansion/contraction of the ball screw.

2. The servo controller as set forth in claim 1, further comprising a distance calculating part which calculates the distance from the servomotor to the movable body threadably engaged with the ball screw, by using an angular position of the servomotor.

3. The servo controller as set forth in claim 2, wherein the distance calculating part utilizes a parameter which is previously determined based on a dimension of each component so as to represent a relationship between the distance from the movable body to the servomotor and a rotational angular position of the ball screw, and calculates the distance from the movable body to the servomotor in real-time at the angular position of the servomotor detected by the position detecting part.

4. The servo controller as set forth in claim 1, wherein the amount of position correction calculating part calculates the amount of expansion/contraction of the ball screw by multiplying the distance from the servomotor to the movable body by the torque command value so as to obtain a product, and by further multiplying the product by a first coefficient relating to the ball screw.

5. The servo controller as set forth in claim 1, wherein the amount of position correction calculating part calculates the amount of position correction as a summation of:

(i) the amount of expansion/contraction of the ball screw which is obtained by multiplying the distance from the servomotor to the movable body by the torque command value so as to obtain a product, and by further multiplying the product by a first coefficient relating to the ball screw; and

(ii) a positioning error which is obtained by multiplying the torque command value by a second coefficient relating to a coupling for coupling the servomotor and the ball screw.