External force judgment method and external force judgment device of human-collaborative industrial robot

An external force judgment device for judging a presence or absence of an external force acting on a robot including a first member and a second member movably connected to the first member through a deceleration mechanism, the device comprising:

• a reference value acquisition unit for acquiring a reference value of a relative position or angle of the second member with respect to the first member when the robot on which no external force is acting or on which a known external force is acting is assumed to be operated or is operated by a predetermined command in advance;
• a measured value acquisition unit for acquiring a measured value of the relative position or angle of the second member with respect to the first member when the robot is operated by the predetermined command, the measured value acquisition unit including a detection unit and a detected unit paired with the detection unit, wherein, one of the detection unit and the detected unit is arranged on the first member or a part not relatively moving with respect to the first member, whereas another of the detection unit and the detected unit is arranged on the second member or a part not relatively moving with respect to the second member, and a value detected by the detection unit is the measured value;
• and
• a judgment unit for judging the presence or absence of an external force acting on the robot based on a difference between the reference value acquired by the reference value acquisition unit and the measured value acquired by the measured value acquisition unit and a predetermined threshold value.