Servo controlling device and method

• US 20030139824A1
• Filed: 12/31/2002
• Published: 07/24/2003
• Est. Priority Date: 03/27/2000
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Yaskawa Denki
• Original Assignee: Kabushiki Kaisha Yaskawa Denki
• Inventors: Tsuruta, Kazuhiro, Akamatsu, Keizo
• Granted Patent: US 7,050,862 B2
• Time in Patent Office: Days
• 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=∫

_a^a w(t)(Tref(t)−

T′

ref(t))²dt (w(t)≧

0, a≦

tz≦

b)

provided that an actual torque instruction is defined as T′

ref (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.