Abstract: Aiming at the problem that the continuous fiber reinforced composite material has no tension or the tension can only be adjusted in one direction during the additive manufacturing process, a bidirectional control method for the tension in continuous fiber additive manufacturing was proposed. A bidirectional PID closed-loop control experiment platform for continuous fiber additive manufacturing with Siemens 1200-1217 PLC controller as the core, servo motor as the execution element and tension sensor as the detection element was built. The irregular movement of the printing nozzle of continuous fiber additive manufacturing was equivalently simulated by the forward and reverse movement of the fiber roller driven by the stepper motor. Through automatic adjustment and manual tuning of PID parameters, PID parameters that can stably control the tension within a certain range were obtained. Without the gravity stable module, the control accuracy of the tension control system at different take-up speeds and different tension setting values, as well as the control ability of the system when the take-up roller under the conditions of forward acceleration, reverse acceleration, and forward/reverse mixed speed change were studied. After adding the gravity stabilization module, its effect on stabilizing tension when the take-up speed switches instantaneously between forward and reverse was studied. The research results show that the control accuracy of the system can reach up to ±0.22 N, and it has a rapid adjustment function when the take-up roller is switched between forward and reverse at a certain speed. The addition of gravity stabilization device can reduce the sudden change of tension caused by the instantaneous excessive speed change, and has a stabilizing effect on the tension control system.

Key words: continuous fiber, additive manufacturing, tension, bidirectional PID control, closed-loop control, gravity stabilization device, composites