A harmonic drive actuator is a device that converts electrical energy into mechanical energy to achieve rotational motion of mechanical parts. Its core technologies include a motor, a harmonic reducer, and sensors. As the core component of a rotary actuator, the motor is responsible for converting electrical energy into mechanical energy to achieve the rotation of the mechanical parts; the reducer reduces the motor speed and increases torque to meet the needs of various application scenarios; and the sensors monitor the actuator's position and speed to achieve closed-loop control. Rotary actuators are widely used in various joints and drive components of humanoid robots, such as the head, neck, waist, arms, and legs. By using rotary actuators, humanoid robots can perform various complex movements such as walking, bending, grasping, and manipulating. In addition, rotary actuators can also be used in other automated equipment and intelligent devices, such as machine tools, automated production lines, and drones.