Robot system with a torque sensor

A robot system, comprising:

• a robot that comprises one or more joints;
• and
• a control device that is connected to the robot and that comprises at least one processor,
• wherein the joints each comprise;
• a motor;
• a speed reduction mechanism that comprises a plurality of speed-reduction elements connected with each other, the plurality of speed-reduction elements including a first speed-reduction element connected to the motor;
• and
• a torque sensor that detects, as an actual torque, an output torque of the speed reduction mechanism,
• wherein the speed reduction mechanism is configured to reduce a speed of revolution of the motor at a plurality of reduction ratios each of which is associated with each of the plurality of speed-reduction elements, and
• wherein the at least one processor is configured to:
• operate the motor by a predetermined current value and obtain the number of revolutions of the motor;
• calculate an ideal torque that is an ideal output torque of the speed reduction mechanism when operating the motor by the predetermined current value;
• obtain time-series data about a first differential torque that is a difference between time-series data about the ideal torque and time-series data about the actual torque;
• extract a frequency of a periodic component contained in the time-series data about the first differential torque;
• and
• sequentially compare a value obtained by dividing the number of revolutions by the extracted frequency with each of a plurality of predetermined values determined based on the plurality of reduction ratios so as to identify, of the plurality of speed-reduction elements, a speed-reduction element that has a problem.