Abstract
Joint clearances in antenna pointing mechanisms lead to uncertainty in function deviation. Current studies mainly focus on radial clearance of revolute joints, while axial clearance has rarely been taken into consideration. In fact, owning to errors from machining and assembly, thermal deformation and so forth, practically, axial clearance is inevitable in the joint. In this study, an error equivalent model (EEM) of revolute joints is proposed with considering both radial and axial clearances. Compared to the planar model of revolute joints only considering radial clearance, the journal motion inside the bearing is more abundant and matches the reality better in the EEM. The model is also extended for analyzing the error distribution of a spatial dual-axis (“X–Y” type) antenna pointing mechanism of Spot-beam antennas which especially demand a high pointing accuracy. Three case studies are performed which illustrates the internal relation between radial clearance and axial clearance. It is found that when the axial clearance is big enough, the physical journal can freely realize both translational motion and rotational motion. While if the axial clearance is limited, the motion of the physical journal will be restricted. Analysis results indicate that the consideration of both radial and axial clearances in the revolute joint describes the journal motion inside the bearing more precise. To further validate the proposed model, a model of the EEM is designed and fabricated. Some suggestions on the design of revolute joints are also provided.
Highlights
In order to achieve real-time tracking and precise pointing on target satellites, dual-axis antenna pointing mechanisms have been widely applied in communication satellites and data relay satellites for satellite-ground and satellite-satellite communication and data transmission
Bai et al [15] established a hybrid contact force model to forecast the dynamic performance of planar mechanical systems with revolute joint clearances
6 Conclusions In this paper, an equivalent model (EEM) of the revolute joint with clearances is proposed by the virtual bar method
Summary
In order to achieve real-time tracking and precise pointing on target satellites, dual-axis antenna pointing mechanisms have been widely applied in communication satellites and data relay satellites for satellite-ground and satellite-satellite communication and data transmission. Bai et al [15] established a hybrid contact force model to forecast the dynamic performance of planar mechanical systems with revolute joint clearances. Brutti et al [19] presented a general computer-aided model of a 3D revolute joint with clearances suitable for implementation in multi body dynamic solvers. Taking both radial and axial clearances into consideration, Yan et al [20] established a synthetic model for 3D revolute joints with clearances in mechanical systems by the contact force approach. Based on the contact force approach, Marques et al [21, 22] presented a formulation to model spatial revolute joints with radial and axial clearances. The model is more intuitive and graphic than the 3D contact force model of revolute joints in Refs. [20,21,22] and it is easier to be applied to analysis of pointing accuracy of the spatial dual-axis pointing mechanism (Additional file 1)
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