Accuracy Compensation Technology of Closed⁃Loop Feedback of Industrial Robot Joints

The existing kinematic parameter calibration method cannot further improve the absolute positioning accuracy of the robot due to the uncertainty of positioning error caused by robot joint backlash.In view of this problem,a closed‑loop feedback accuracy compensation method for robot joints was proposed.Firstly,a Chebyshev polynomial error estimation model was established which took geometric error and non‑geometric error into account.In addition,the absolute linear grating scale was installed at each joint of the robot and the positioning error of the robot end was mapped to the joint angle.And the joint angle corrected value was obtained.Furthermore,the closed‑loop feedback of robot joints was established to realize the online correction of the positioning error.Finally,an experiment on the KUKA KR210 industrial robot was conducted to demonstrate the effectiveness of the method.The result shows that the maximum absolute positioning error of the robot is reduced by 75%from 0.76 mm to 0.19 mm.This method can compensate the robot joint backlash effectively and further improve the absolute positioning accuracy of the robot.

Non-linear Dynamics Method to Angles-Only Navigation for Non-cooperative Rendezvous of Spacecraft

Aiming at the problem of relative navigation for non-cooperative rendezvous of spacecraft,this paper proposes a new angles-only navigation architecture using non-linear dynamics method. This method does not solve the problem of poor observability of angles-only navigation through orbital or attitude maneuvering,but improves the observability of angles-only navigation through capturing the non-linearity of the system in the evolution of relative motion. First,three relative dynamics models and their corresponding line-of-sight(LoS)measurement equations are introduced,including the rectilinear state relative dynamics model,the curvilinear state relative dynamics model,and the relative orbital elements(ROE)state relative dynamics model. Then,an observability analysis theory based on the Gramian matrix is introduced to determine which relative dynamics model could maximize the observability of angles-only navigation. Next,an adaptive extended Kalman filtering scheme is proposed to solve the problem that the angles-only navigation filter using the non-linear dynamics method is sensitive to measurement noises. Finally,the performances of the proposed angles-only navigation architecture are tested by means of numerical simulations,which demonstrates that the angles-only navigation filtering scheme without orbital or attitude maneuvering is completely feasible through improving the modeling of the relative dynamics and LoS measurement equations.

Analysis of safety characteristics of coal-based aviation kerosene

The risk and thermal safety characteristics of GX kerosene,HX kerosene and WX kerosene are studied.Firstly,the explosion lower limits of three kinds of kerosene steams are tested by using the self-made explosion limit measuring system.Then differential scanning calorimeter(DSC)is employed to perform linear heating experiment on kerosene to analyze its thermal decomposition characteristics.The pyrolysis kinetic parameters of three kinds of kerosene are calculated based on the thermal dynamic methods.The experimental results show that the flash point and lower explosion limit of GX kerosene are relatively low.The DSC test shows that the lowest initial decomposition temperature of HX kerosene is 116.5℃.According to pyrolysis kinetics calculation,the T_(D24) and apparent activation energy of HX kerosene are the minimum.ARC test shows that GX kerosene has the worst thermal stability under the adiabatic condition.The high temperature stabilities of the three kinds of kerosene all meet the requirements.On the whole,GX kerosene has the highest hazard,and HX kerosene has the lowest thermal safety.The accumulation of heat should be prevented during the storage and transportation of kerosene.This study provides the crucial safety characteristics data of coal-based aerospace kerosene-based,and provides technical support for engine reliability growth and performance improvement.

Flow and Leakage Characteristics in Sealing Chamber of a Variable Geometry Hypersonic Inlet

When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber,the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out.The results show that three-dimensional cavity flow structures are close to being asymmetric,and the entrance pressure of the leakage path can also be affected by asymmetry;with the increase of the thickness of the boundary layer,the pressure at the cavity floor and the seal entrance decreases.Finally,the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.

Methods for Reducing Interface Aperture Inconsistency During NC Orbital Milling of Aircraft Laminates with Coarse Pitch

The methods for reducing interface aperture inconsistency are studied in NC orbital milling(NCOM)of CFRP/Ti6Al4V laminates with coarse pitch.Comparative experiments show burr,aperture inconsistency and error are typical interface defects.Meanwhile,aperture inconsistency and error are more serious than burr in NCOM with coarse pitch.As one of the major causes of interface defects,axial force and radial force are intensively studied.Based upon the machining principle of orbital milling(OM)and the actual hole-making condition in laminated structures,NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions.Then,the effects of interlayer clamping,minimal quantity lubrication(MQL),twice milling instead of reaming,and interlayer speed change on interface aperture are analyzed.Research shows that interlayer clamping,interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture.When making holes of different diameters with one cutter,axial feed has a greater effect on interface aperture precision than tangential feed.When making holes of the same diameter with different cutters,small diameter cutter will reduce interface aperture precision in a single processing.But the method of“twice milling instead of reaming”can improve the aperture precision effectively.

Mapping relationship analysis of welding assembly properties for thin-walled parts with finite element and machine learning algorithm

The finite element(FE)-based simulation of welding characteristics was carried out to explore the relationship among welding assembly properties for the parallel T-shaped thin-walled parts of an antenna structure.The effects of welding direction,clamping,fixture release time,fixed constraints,and welding sequences on these properties were analyzed,and the mapping relationship among welding characteristics was thoroughly examined.Different machine learning algorithms,including the generalized regression neural network(GRNN),wavelet neural network(WNN),and fuzzy neural network(FNN),are used to predict the multiple welding properties of thin-walled parts to mirror their variation trend and verify the correctness of the mapping relationship.Compared with those from GRNN and WNN,the maximum mean relative errors for the predicted values of deformation,temperature,and residual stress with FNN were less than 4.8%,1.4%,and 4.4%,respectively.These results indicate that FNN generated the best predicted welding characteristics.Analysis under various welding conditions also shows a mapping relationship among welding deformation,temperature,and residual stress over a period of time.This finding further provides a paramount basis for the control of welding assembly errors of an antenna structure in the future.