Device and method for diagnosing failure of speed reducer

A failure diagnosing device configured to diagnose failure of a plurality of reduction gears provided to a mechanical apparatus including a plurality of operation components, and a plurality of motors configured to drive the plurality of operation components, respectively, the plurality of reduction gears being configured to reduce speeds of rotational forces of the plurality of motors and transmit the reduced rotational forces to the plurality of operation components, respectively, the failure diagnosing device comprising:

• acceleration/deceleration period identifying circuitry configured to identify an acceleration/deceleration period of operation of one component of the plurality of operation components;
• motor current processing circuitry configured to process motor current to acquire a peak value of an amplitude of a frequency component of the motor current in a specific frequency band during the acceleration/deceleration period (hereinafter, referred to as “the amplitude peak value of the motor current”), the motor current being one of a load current of one of the motors configured to drive the one operation component and a current value having a correlation with the load current;
• and
• determining circuitry configured to determine, based on the amplitude peak value of the motor current, whether a sign of failure exists in one of the reduction gears configured to reduce the speed of the rotational force of the one motor and transmit the reduced rotational force to the one operation component,
• wherein the mechanical apparatus is provided with a plurality of natural frequencies, and one specific frequency band includes one of the natural frequencies at which the mechanical apparatus is oscillated by resonance in a meshing direction of a gear of the one reduction gear, and
• wherein the determination is performed for each of the plurality of reduction gears.