Robot control apparatus for monitoring load on robot

• US 5,587,635 A
• Filed: 05/30/1995
• Issued: 12/24/1996
• Est. Priority Date: 09/30/1993
• Status: Expired due to Term

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Watanabe, Atsushi, Nihei, Ryo, Terada, Akihiro
• Primary Examiner(s): Cabeca, John W.
• Application Number:
  US08/446,713
• Time in Patent Office: 574 Days
• Field of Search: 318/649, 318/611, 318/798, 318/254, 318/138, 318/432, 318/433, 318/617, 318/618, 318/431, 318/139, 318/276, 318/271, 318/434, 318/568.25, 318/689, 318/635, 388/930
• US Class Current: 318/434
• CPC Class Codes: G05B 19/4065 Monitoring tool breakage, life or condition
• CPC Class Codes: G05B 2219/37209 Estimate life of gear, drive
• CPC Class Codes: G05B 2219/37344 Torque, thrust, twist, machining force measurement
• CPC Class Codes: G05B 2219/45083 Manipulators, robot
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

A robot control apparatus in which a load exerted on a driving system of a robot is detected to make it easy to judge a time for preventive maintenance or overhaul, and life of the robot driving system. A driving torque Ta outputted to the driving system is found by subtracting a torque which is spent in a motor itself for accelerating or decelerating a rotor from an output torque T of a motor M for driving each axis of the robot. Further, an average torque of the driving torque Ta and an average speed of an output shaft of the motor M are found and displayed. An average torque of an output torque of a speed reducer and an average speed of an output shaft of the speed reducer are obtained, and, based on these values, the life of the speed reducer is determined. Then a ratio of the determined life to a rated life is obtained and displayed. An actual load exerted on the driving system is monitored, so that the time for the preventive maintenance or overhaul, and life of the driving system is easily judged. Also, the life of the speed reducer is easily predicted.

Claims

1. A robot control apparatus for monitoring a load exerted on a robot comprising:

a motor having an output shaft connected to a driving mechanism of said robot;

speed detection means for detecting a rotational angular speed of said motor;

acceleration calculation means for determining a rotational angular acceleration of said motor based on said rotational angular speed;

driving torque calculation means for calculating a driving torque outputted from said motor output shaft by determining a torque spent inside the motor using said rotational angular speed and said rotational angular acceleration, by determining a torque generated by the motor using a driving current of said motor and by subtracting said torque spent inside the motor from said torque generated by said motor; and

display means for displaying said calculated driving torque.

2. A robot control apparatus according to claim 1, further comprising means for determining an average driving torque of said motor output shaft based on the motor rotational angular speed and said driving torque, wherein said display means further displays said average driving torque.

3. A robot control apparatus according to claim 1, further comprising:

sampling means for sampling the motor rotational angular speed and the motor driving current at each predetermined period during an operation of each shaft of said robot driving mechanism;

means for calculating an average rotational speed of the motor at each said predetermined period based on said motor rotational angular speed sampled by said sampling means;

means for counting a number of times of said sampling until each said predetermined period;

means for determining a total operating period of time during which said shaft is in operation by multiplying said counted number of times of sampling by a sampling period; and

means for determining an average driving torque at each said predetermined period using said motor rotational angular speed, said driving torque obtained by said driving torque calculation means, an average driving torque obtained at an immediately preceding said predetermined period, said average rotational speed, the total operating period of time and said predetermined period,

wherein said display means further displays said average driving torque.

4. A robot control apparatus according to claim 3, wherein said sampling means samples a motor driving current based on a move command to each shaft of said driving mechanism according to an operation program of said robot.

5. A robot control apparatus according to claim 3, wherein said driving mechanism comprises a speed reducer, said robot control apparatus further comprises means for determining an average torque and an average revolution speed of an output shaft of said speed reducer based on said average driving torque, said average rotational speed of said motor and a reduction ratio of said speed reducer, and said display means further displays the average torque and the average revolution speed of the output shaft of said speed reducer.

6. A robot control apparatus according to claim 5, further comprising:

means for determining a rated life period of said speed reducer based on a rated torque and a rated revolution speed of said speed reducer, and said average torque and said average revolution speed of the output shaft of said speed reducer; and

means for determining a rated life ratio by dividing said total operation period by said rated life period, wherein said display means further displays said rated life ratio.

7. A robot control apparatus according to claim 2, wherein said means for determining the average driving torque Tm obtains a cubic mean of said driving torque Ta when a structure of said driving system is based on ball bearings, and determines a 10/3 power mean of said driving torque Ta when the structure of said driving system is based on roller bearings, and wherein said display means further displays said cubic mean and 10/3 power mean.

8. A robot control apparatus as set forth in claim 1, further comprising memory means for storing maximum values of said driving torque and said motor rotational speed, wherein the maximum values stored in said memory means are updated when said driving torque and said motor rotational speed are larger than the respective maximum values stored in said memory means, and said display means further displays said maximum driving torque and said maximum motor rotational speed.