Machine having movable unit to be controllably driven by servo motor

• US 20070052383A1
• Filed: 08/03/2006
• Published: 03/08/2007
• Est. Priority Date: 09/08/2005
• Status: Active Grant

• Current Assignee: Aiwa International Patent Agency
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Abe, Hiroyuki, Ogata, Toshiyuki, Kawamura, Hiroyuki
• Granted Patent: US 7,638,964 B2
• Time in Patent Office: Days
• US Class Current: 318/651
• CPC Class Codes: G05B 19/4062 Monitoring servoloop, e.g. overload of servomotor, loss of feedback or reference
• CPC Class Codes: G05B 2219/37626 By measuring changing forces in different position zones
• CPC Class Codes: G05B 2219/37632 By measuring current, load of motor

Abstract

A speed region of a motor is divided into a region lower than a first switch speed VS1, a region higher than a second switch speed VS2 and a region between the first and second switch speeds. An abnormal load determination level to be compared with an estimated load obtained by an observer is set for each of the regions. An abnormal load determination level AL4 applied when an acceleration exceeds a threshold value is set. The abnormal load determination level AL4 is used for comparison with the estimated load until a predetermined period of time elapses after the acceleration to be commanded to the motor, which once exceeded the threshold level, drops. In other cases, the estimated load is compared with the abnormal load determination level having a value according to the speed. If the estimated load exceeds the compared abnormal load determination level, it is judged that a collision is detected.

Claims

1. A machine having a movable unit to be controllably driven by a servo motor, comprising:

load torque estimating means for estimating a load to be exerted on the servo motor;

means for obtaining an acceleration based on a command given to the servo motor;

means for storing therein an abnormal load determination level at the time of increase in acceleration;

acceleration comparing means for comparing the obtained acceleration with a set acceleration threshold value, so as to output a signal when the acceleration exceeds the acceleration threshold value; and

abnormal load determining means for comparing the stored abnormal load determination level with the load torque estimated by the load torque estimating means when the signal is output from the acceleration comparing means, so as to issue an alarm when the estimated load torque exceeds the abnormal load determination level at the time of increase in acceleration.

2. The machine having the movable unit to be controllably driven by the servo motor according to claim 1, further comprising:

clocking means for measuring a lapse of time after the obtained acceleration, which has once exceeded the acceleration threshold value, drops to the level lower than the acceleration threshold value,

wherein the abnormal load determining means compares the abnormal load determination level at the time of increase in acceleration with the estimated load torque until a predetermined period of time is measured by means of the clocking means after the acceleration exceeds the acceleration threshold value.

3. The machine having the movable unit to be controllably driven by the servo motor according to claim 1, further comprising:

storing means for storing therein the abnormal load determination level according to speeds;

speed detecting means for detecting a speed in the servo motor or the movable unit; and

means for selecting the abnormal load determination level according to the speed detected by means of the speed detecting means,

wherein the abnormal load determining means, when it does not compare the abnormal load determination level at the time of increase in acceleration with the estimated load torque since there is no output of the signal from the acceleration comparing means, reads an abnormal load determination level corresponding to the speed detected by the speed detecting means, from the storing means, compares the read abnormal load determination level with the estimated load torque, and issues an alarm if the estimated load torque exceeds the read abnormal load determination level.

4. The machine having the movable unit to be controllably driven by the servo motor according to claim 3, wherein speed is divided into a plurality of regions and the abnormal load determination level corresponding to the speed is set for each region.

5. The machine having the movable unit to be controllably driven by the servo motor according to claim 1, further comprising:

means for obtaining an abnormal load determination level corresponding to speed on the basis of a function;

speed detecting means for detecting a speed in the servo motor or the movable unit; and

means for selecting the abnormal load determination level according to the speed detected by the speed detecting means,

wherein the abnormal load determining means, when it does not compare the abnormal load determination level at the time of increase in acceleration with the estimated load torque since there is no output of the signal from the acceleration comparing means, obtains an abnormal load determination level corresponding to the speed detected by means of the speed detecting means on the basis of the function, compares the obtained abnormal load determination level with the estimated load torque, and issues an alarm if the estimated load torque exceeds the read abnormal load determination level.

6. The machine having the movable unit to be controllably driven by the servo motor according to claim 1, wherein the abnormal load determination level is set based on the estimated load torque generated when the movable unit is operated in a predetermined manner.

7. The machine having the movable unit to be controllably driven by the servo motor according to claim 1, wherein a warning is noticed when the estimated load torque exceeds a warning level smaller by a predetermined quantity than the abnormal load determination level.

8. A machine having a movable unit to be controllably driven by a servo motor comprising:

detecting means for detecting a position and a speed of the movable unit;

means for calculating a command acceleration based on a position command to be given to the servo motor;

storing means for storing therein a first abnormal load determination level which is applied when the calculated command acceleration is equal to or greater than a preset acceleration value, and a second abnormal load determination level which has a value according to the detected speed and is applied when the calculated command acceleration is lower than the preset acceleration value;

a disturbance load observer for estimating a disturbance load based on the position command and the detected position and speed;

comparing/reading means for comparing the command acceleration with the preset acceleration value and reading the first abnormal load determination level or the second abnormal load determination level stored in the storing means based on the comparison result; and

alarm issuing means for comparing the abnormal load determination level read by the comparing/reading means with the disturbance load estimated by means of the disturbance load observer and issuing an alarm if the estimated disturbance load exceeds the abnormal load determination level.