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Abnormality determining device and abnormality determining method

  • US 10,335,948 B2
  • Filed: 03/30/2017
  • Issued: 07/02/2019
  • Est. Priority Date: 04/18/2016
  • Status: Active Grant
First Claim
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1. An abnormality determining device that determines abnormality of a reduction gear of a motor for a robot including:

  • a jointed arm having a joint rotating in a pitch direction that is driven by the motor via the reduction gear, and a balancer provided to the joint, the balancer being configured to generate a balancing force for balancing a gravitational moment acting on the joint, the abnormality determining device comprising;

    a processor programmed to;

    detect a current value which is a value of a drive current of the motor;

    group time-series current values detected in time series at a predetermined time interval of greater than 10 ms, to calculate a variance value of the current values of each group, and to calculate a variance ratio of each group by dividing the variance value of the current values of a corresponding group by a variance value of a reference current value of the motor when the reduction gear is new;

    detect a rotational angular velocity of the motor;

    detect a rotation angle of the motor;

    determine that the reduction gear is abnormal when the calculated variance ratio is equal to or greater than a threshold value;

    calculate a variation of rotational angular velocities corresponding to the current values of the motor in the groups based on the detected rotational angular velocity of the motor;

    extract groups in which a calculated variation of the rotational angular velocities of the motor is equal to or less than a predetermined variation from the groups;

    extract groups in which all the rotation angles corresponding to the current values belonging to each group are within a predetermined angle range centered on a neutral rotation angle at which the gravitational moment balances with the balancing force;

    calculate an abnormality ratio which is a ratio of a number of groups in which the variance ratio is equal to or greater than the threshold value to a number of groups using only the variance ratios of the extracted groups;

    determine that the reduction gear is abnormal when the calculated abnormality ratio is equal to or greater than a predetermined ratio; and

    when it is determined that the reduction gear is abnormal, issue a report that the reduction gear is abnormal.

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