Abstract: To address the assembly operation challenges of existing bolt assembly robots in confined spaces, a lightweight and compact automatic assembly actuator mounted on the robot end-effector is developed, and an STM32 microcontroller unit (MCU) based voltage and current double closed-loop control system is designed. During the automatic bolt propulsion and resetting in assembly process, this system can collect voltage and current signals required for the actuator operation in real time. After signal processing, the STM32 MCU generates voltage control signals to precisely regulate the actuator operation. The automatic propulsion and resetting functions in bolt assembly process simplify the motion control of manipulator carrying the actuator. The system indirectly controls the bolt tightening torque by regulating the current. Compared with existing actuator designs relying on torsion sensor feedback control, the actuator size and weight are significantly reduced by the proposed design. Extensive practical tests demonstrate that the automatic actuator can accurately perform automatic installation, disassembly, and tightening operations for M4, M5, and M6 external hexagonal carbon steel bolts.