Abstract
The deformation of riveting machine caused by riveting force during rivet formed makes the riveting tool out of positioning, which leads to gapping underneath the rivet manufactured head and insufficient rivet drive head. This paper proposes a hybrid position/force riveting control method for the dual-machine drilling and riveting system to eliminate the negative effects of machine deformation. The cooperative work of two-side machine tool is realized by a hybrid position/force control strategy, which compensates for the force-induced deformation error without an accurate stiffness model of the riveting system. The position of pressing foot relative to the machine which represents the deformation of skin-side machine is obtained for the compensation to the displacement of skin-side actuator. Simultaneously, the advanced force control is adopted for the stringer-side actuator. The dynamics model of the stringer-side actuator in consideration of the machine deformation is established and identified. The disturbance observer (DOB) and feedforward controller are introduced as the model-based control algorithm to achieve the high-performance force control. Also, contrast experiments are conducted to validate the effectiveness of the proposed riveting control method. The results show that the rivet manufactured head can be seated in the countersink during the forming process and the gapping under the head is eliminated. The driven head height tolerance of ±0.1 mm is achieved by accurate force control.
Highlights
Riveting is the main connection form used in aircraft assembly, which can provide enough tension for the aircraft fuselage to withstand the air pressure and other impact
E legacy process used in traditional riveting control method usually ignores the compensation on the manufactured-head side, so the outside rivet die stays still during the riveting process. e medium chart shows the change in the length gauge data under the traditional position control without compensation, which reflects the machine deformation during riveting. e relative position of the pressing foot and the actuator becomes farther because of the machine deformation, and the length gauge elongates by 0.6 mm. e deformation error will vary with the machine posture, which cannot be compensated accurately by the trial and error method without the use of the outer-loop position compensation
E position curve of riveting die after compensation of pressing foot position is shown as the lower chart in Figure 14. e length gauge signal is introduced into the position closed loop as the compensation after the insertion action. e actual position of the riveting die can be adjusted according to the real-time feedback of the length gauge, and the length of the length gauge stays at 15 mm during riveting and dwelling, which proves that the relative position of the riveting die and the pressing foot remains unchanged, so that the rivet manufactured head is not affected by the machine deformation and is always pressed against the countersink hole to eliminate the gapping under the head
Summary
Riveting is the main connection form used in aircraft assembly, which can provide enough tension for the aircraft fuselage to withstand the air pressure and other impact. (1) A dual-machine riveting system is presented in this paper, and the hybrid position/force control scheme is proposed to solve the force-induced deformation error compensation for the unique dual-machine layout (2) e high-performance force control of the riveting system can be achieved utilizing the system dynamic model, and the model-based control algorithm of DOB and feedforward can be successfully applied to the riveting force control (3) e outer-loop position compensation control based on the special design of the pressure foot can solve the cooperation of dual-machine (4) e filter design in the proposed hybrid position/ force control method is important to suppress the external disturbances, measurement noise, and modeling uncertainty e remainder of this paper is organized as follows. The riveting control method is validated on the dual-machine riveting system, and the contribution of the proposed method is summarized
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