Direct teaching is an essential function for collaborative robots for easy use by non-experts. For most robots, direct teaching is implemented only in joint space because the realization of Cartesian space direct teaching, in which the orientation of the end-effector is fixed while teaching, requires a measurement of the end-effector force. Thus, it is limited to the robots that are equipped with an expensive force/torque sensor. This study presents a Cartesian space direct teaching method for torque-controlled collaborative robots without either a force/torque sensor or joint torque sensors. The force exerted to the end-effector is obtained from the external torque which is estimated by the disturbance observer-based approach with the friction model. The friction model and the estimated end-effector force were experimentally verified using the robot equipped with joint torque sensors in order to compare the proposed sensorless approach with the method using torque sensors.

Abstract
1. 서 론
2. 토크 기반 임피던스 제어
    2.1 말단 힘 추정
    2.2 직교공간 임피던스 제어
3. 센서리스 직접교시
    3.1 마찰모델
    3.2 센서리스 직접교시
4. 실 험
    4.1 마찰모델의 검증
    4.2 센서리스 직교공간 직접교시
5. 결 론
References

• 안국현(Mechanical Engineering, Korea University) | Kuk-Hyun Ahn
• 송재복(Mechanical Engineering, Korea University) | Jae-Bok Song Corresponding author