Modeling and Compensation Technology for the Comprehensive Errors of Fixture System

Error modelling and compensating technology is an effective method to improve the processing precision.The position and orientation deviation of workpiece is caused by the fixing and manufacturing errors of the fixture.How to reduce the position and orientation deviation of workpiece has become a technical problem of improving the processing quality of workpiece.In order to increase machining accuracy,an implementation scheme of fixture system comprehensive errors（FSCE） compensation is proposed.A FSCE parameter model is established by analyzing the influence of contact points on the position and orientation of workpiece.Meanwhile,a parameter identification method for FSCE parameter model is presented by using the 3-2-1 deterministic positioning fixture,which determines the model parameters.Moreover,a FSCE compensation model is formulated to study the compensation value of the cutting position.By using RenishawOMP60 Probe and combining vertical machining centre（SKVH850） equipment with SKY2001 Open CNC System,on-machine verification system（OMVS） is built to measure FSCE successfully.The processing error can be reduced by analyzing the cutting position of the tool with the homogeneous transformation of space coordinate system.Finally,the compensation experiment of real time errors is conducted,and the cylindricality and perpendicularity errors of hole surface are reduced by 30.77% and 28.57%,respectively.This paper provides a new way of realizing the compensation of FCSE,which can improve the machining accuracy of workpiece largely.

CALIBRATION OF A 6-DOF SPACE ROBOT USING GENETIC ALGORITHM

The kinematic error model of a 6-DOF space robot is deduced, and the cost function of kinematic parameter identification is built. With the aid of the genetic algorithm （GA） that has the powerful global adaptive probabilistic search ability, 24 parameters of the robot are identified through simulation, which makes the pose （position and orientation） accuracy of the robot a great improvement. In the process of the calibration, stochastic measurement noises are considered. Lastly, generalization of the identified kinematic parameters in the whole workspace of the robot is discussed. The simulation results show that calibrating the robot with GA is very stable and not sensitive to measurement noise. Moreover, even if the robot＇s kinematic parameters are relative, GA still has strong search ability to find the optimum solution.

An approach to measure the pose of RHJD4-1 arc welding robot for calibration

A measurement setup used for robot calibration was designed to meet the requirement of off line programming technique. The robot end effector pose (position and orientation) can be calculated indirectly by using this setup. The setup has been applied to RHJD4 1 arc welding robot. The experimental results show the method of pose measuring using the measurement setup is simple and reliable to finish pose measuring for robot calibration. In addition, the setup can measure the position repeatability of robot.

A novel approach to minimizing material loss for computer numerical control flank-regrinding of worn end mills

Flanks of end mills are prone to wear in a long machining process.Regrinding is widely used in workshops to restore the flank to an original-like state.However,the traditional method involves material waste by trial and error and dramatically decreases the potential regrinding.Moreover,over-cut would happen to the flutes of worn cutters in the regrinding processes because of improper wheel path.This study presented a new approach to planning the wheel path for regrinding worn end mills to minimize material loss and recover the over-cut.In planning,a scaling method was developed to determine the maximum size of the new cutter according to the similarity of cutter shapes before and after regrinding.Then,the wheel path is first generated by envelope theory to regrind the worn area with a four-axis computer numerical control grinder according to the new size of cutters.Moreover,a second regrinding strategy is applied to recover the flute shape over-cut in the first grinding.Finally,the proposed method is verified by an experiment.Results showed that the proposed approach could save 25%of cutter material compared with the traditional method and ensure at least three regrinding times.This work effectively provides a general regrinding solution for the worn flank with maximum material-saving and regrinding period.

Research on uncertainty in measurement assisted alignment in aircraft assembly

Operations in assembling and joining large size aircraft components are changed to novel digital and flexible ways by digital measurement assisted alignment.Positions and orientations（P＆O）of aligned components are critical characters which assure geometrical positions and relationships of those components.Therefore,evaluating the P＆O of a component is considered necessary and critical for ensuring accuracy in aircraft assembly.Uncertainty of position and orientation（U-P＆O）,as a part of the evaluating result of P＆O,needs to be given for ensuring the integrity and credibility of the result;furthermore,U-P＆O is necessary for error tracing and quality evaluating of measurement assisted aircraft assembly.However,current research mainly focuses on the process integration of measurement with assembly,and usually ignores the uncertainty of measured result and its influence on quality evaluation.This paper focuses on the expression,analysis,and application of U-P＆O in measurement assisted alignment.The geometrical and algebraical connotations of U-P＆O are presented.Then,an analytical algorithm for evaluating the multi-dimensional U-P＆O is given,and the effect factors and characteristics of U-P＆O are discussed.Finally,U-P＆O is used to evaluate alignment in aircraft assembly for quality evaluating and improving.Cases are introduced with the methodology.

Calibration of digital camera integration accuracy for low-cost oblique aerial photogrammetry

This work describes a calibration process for inexpensive consumer cameras integrated into a low cost and compact aerial multi-view imager for remote sensing and photogrammetry.The main advantage of this design is to make the filming component lightweight and rapidly deployable,as well as reducing cost when compared with mainstream commercial oblique imagery.An in situ flight test was carried out in Guiyang.In that experiment,a meridian convergence-based approach was adopted to adjust preprocessing,the residue error and the captured images’exterior orientation linear and angular parameters were calculated by means of the direct geo-referencing approach yielding a favorable outcome for exterior orientation linear parameters of the camera,around 0.2–0.3 m deviation from the actual measured results at 1000 m flight above ground level.The camera’s exterior orientation angular parametersφ,ωwhose difference compared with the standard aerial aero triangulation approach reached a high accuracy level within the intended endurance of 0.005°.These results indicate that the compact implementation of the oblique aerial imager comprised of consumer level off-the-shelf digital cameras achieved competitive accuracy at a low cost and high versatility.