Servo controlling device and method

• US 7,050,862 B2
• Filed: 03/26/2001
• Issued: 05/23/2006
• Est. Priority Date: 03/27/2000
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Yaskawa Denki
• Original Assignee: Kabushiki Kaisha Yaskawa Denki
• Inventors: Tsuruta, Kazuhiro, Akamatsu, Keizo
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): Lee, Douglas S.
• Application Number:
  US10/239,776
• Publication Number:
  US 20030139824A1
• Time in Patent Office: 1,884 Days
• Field of Search: 700/29, 700/69, 700/186, 318/560, 318/561, 318/568.11, 318/568.18
• US Class Current: 700/29
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 19/231 the positional error is used to control continuously the servomotor according to its magnitude
• CPC Class Codes: G05B 19/251 the positional error is used to control continuously the servomotor according to its magnitude
• CPC Class Codes: G05B 2219/41161 Adaptive friction compensation
• CPC Class Codes: G05B 2219/42154 Model itself controlled by position and speed loop
• CPC Class Codes: G05B 2219/42155 Model
• CPC Class Codes: G05B 2219/42162 Model reference adaptive control MRAC, correction fictive-real error, position

Abstract

When a position/speed feedback changes while a control system for driving a feed axis uses an integration gain during a shaft stopping, the control system goes unstable to cause a torque instruction to vibrate or diverge. In addition, only a single, narrow-range feed speed can be accommodated to find an out-of-range speed to be insufficient or excessive in compensation effects. After detecting the movement reversal of a feed axis, a control loop is modeled, a virtual internal model computing unit (21) using a constant separate from a constant used in a control loop is configured, a virtual torque instruction (22) computed by this computing unit (21) is added to a torque instruction (16) for driving the feed axis, this adding is terminated when the virtual torque instruction (22) reaches a specified value, and a value (25) of an integrator in a virtual internal model at the adding termination is added to the integrator (14) corresponding to a position/speed feedback loop.

Claims

1. A servo controlling method which has a control loop using a position/speed feedback and drives a feed axis of a machine tool, wherein

after a movement reversal of the feed axis is detected, a control loop is modeled, and a virtual internal model using constants of values that are different from those of the constants used in the control loop;

a virtual torque instruction calculated in the virtual internal model is added to a torque instruction for driving the feed axis;

when said virtual torque instruction reaches a predetermined value, said adding is terminated; and

when the adding is terminated, a value of an integrator within the virtual internal model at this point is added to a corresponding integrator of the position/speed feedback group.

2. The servo controlling method according to claim 1, wherein the predetermined value is determined as a function of time from the point at which the movement removal is detected.

3. A servo controlling device for controlling a motor based on an inputted position instruction, comprising:

a position detecting part for detecting the position of a rotor of said motor as a motor position;

a speed detecting part for detecting the speed of the motor;

a position controlling part which outputs a speed instruction so that the motor position corresponds to said position instruction;

a speed controlling part which outputs a torque instruction so that the motor speed corresponds to said speed instruction;

a current controlling part which inputs said torque instruction and drives the motor by controlling a current;

a disturbance estimating part which estimates a motor stop timing tz when detecting that the motor speed has become zero by monitoring the motor speed, and outputs an estimated disturbance Cs(t) calculated by

Cs(t)=−

Fc₁+(Cs(tz)+Fc₁)exp((t−

tz)/et₁)−

DcVfb(t) in a case where t≦

tz, or

Cs(t)=Fc₂+(Cs(tz)−

Fc₂)exp((tz−

t)/et₂)+DcVfb(t) in a case where t>

tz, provided that the motor speed is defined as Vfb(t), the viscous friction is defined as Dc, the Coulomb friction when the motor speed is positive is defined as Fc₁, the Coulomb friction when the motor speed is negative is defined as Fc₂, a value of an estimated disturbance at the timing tz is defined as Cs(tz), a time constant of the estimated disturbance Cs(t) when the motor decelerates and stops is defined as et₁, and a time constant of the estimated disturbance Cs(t) when the motor accelerates is defined as et₂; and

means for adding the estimated disturbance Cs(t) to the torque instruction.

4. The servo controlling device according to claim 3, wherein

friction parameters Cs(tz), et₁, and et₂ in the estimated disturbance Cs(t) estimated in the disturbance estimating part are set by using a combination optimizing method to values which minimize an evaluation function J expressed by

$J={\int }_{}^{}$

a b ⁢

w ⁡

( t ) ⁢

( Tref ⁡

( t ) - T ′

⁢

ref ⁡

( t ) ) 2 ⁢

⁢

ⅆ

t ⁢

( w ⁡

( t ) ≥

0 , a ≤

tz ≤

b ) ,

provided that an actual torque instruction is defined as Tref(t), an estimated torque instruction is defined as T′

ref(t), and a weighting function is defined as w(t).

5. The servo controlling device according to claim 4, wherein said combination optimizing method is a genetic algorithm.