Robot system and method for controlling robot system

A robot system comprising:

• a robot arm that includes a plurality of joints including a first joint and a second joint;
• a first joint drive unit that has a first motor having an output shaft connected to the first joint to rotate the first joint;
• a first sensor that obtains information on actual operation of the output shaft of the first motor;
• circuitry that calculates a first current value to be supplied to the first motor based on a deviation between a first operation target for the first motor that is input from a higher device and the actual operation of the output shaft of the first motor, and controls operation of the output shaft of the first motor by supplying current to the first motor based on the first current value;
• a second joint drive unit that has a second motor having an output shaft connected to the second joint to rotate the second joint;
• and
• a second sensor that obtains information on actual operation of the output shaft of the second motor, wherein
• the circuitry calculates a second current value to be supplied to the second motor based on a deviation between a second operation target for the second motor that is input from the higher device and the actual operation of the output shaft of the second motor, and controls operation of the output shaft of the second motor by supplying current to the second motor based on the second current value,
• the circuitry estimates an error in operation of the second joint due to bending and/or twisting of the robot arm based on the first current value, the actual operation of the output shaft of the first motor, and the smallest natural frequency among a plurality of natural frequencies of coupled vibrations of a system including the first joint and the second joint due to bending and/or twisting of the robot arm, and
• the circuitry calculates the second current value so as to control the operation of the output shaft of the second motor in a manner compensating for the error in operation of the second joint due to bending and/or twisting of the robot arm.