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Robotic drilling technology for aircraft flexible assembly has challenges and is under active investigation. In this work, a robotic drilling end-effector is designed and its normal adjustment system is dynamically modeled for comparison of advanced control strategies in terms of position tracking precision and dynamic quality. Three control algori...
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Citations
... Due to the large size and complex profile of the parts of aircraft to be assembled, such as the wing, fuselage, engine and so on, it is difficult for traditional multiaxis machining centers to meet the flexibility of manufacturing and assembly of such large and complex structural parts. Robotic drilling has advantages of high efficiency, spatial accessibility, stability, flexibility and a fast refactoring capability for the assembly of large parts with complex shapes [2,3]. ...
Vibrations in the aircraft assembly building will affect the precision of the robotic drilling system. A variable stiffness and damping semiactive vibration control mechanism with quasi-zero stiffness characteristics is developed. The quasi-zero stiffness of the mechanism is realized by the parallel connection of four vertically arranged bearing springs and two symmetrical horizontally arranged negative stiffness elements. Firstly, the quasi-zero stiffness parameters of the mechanism at the static equilibrium position are obtained through analysis. Secondly, the harmonic balance method is used to deal with the differential equations of motion. The effects of every parameter on the displacement transmissibility are analyzed, and the variable parameter control strategies are proposed. Finally, the system responses of the passive and semiactive vibration isolation mechanisms to the segmental variable frequency excitations are compared through virtual prototype experiments. The results show that the frequency range of vibration isolation is widened, and the stability of the vibration control system is effectively improved without resonance through the semiactive vibration control method. It is of innovative significance for ambient vibration control in robotic drilling systems.
In manufacturing operations such as clamping and drilling of elastic structures, tool-workpiece normality must be maintained, and shear forces minimized to avoid tool or workpiece damage. The challenge is that the combined stiffness of a robot and workpiece, needed to control the robot-workpiece elastic interactions are often difficult to model and can vary due to geometry changes of the workpiece caused by large deformations and associated pose variations of the robot. The main contribution of this article is an algorithm, (i) to learn the robot-workpiece stiffness relationship using a model-free databased approach and (ii) to use it for applying desired forces and torques on the elastic structure. Moreover, comparative experiments with and without the data-based stiffness estimation show that clamping operating speed is increased by four times when using the stiffness estimation method while interaction forces and torques are kept within acceptable bounds.
