| Freeform surface is becoming increasingly widespread in modern industrial manufacturing,but its complexity and diversity,meanwhile,bring new challenges to surface measurement.Five-axis inspection,which can realize continuous scanning on surface,is commonly used in freeform surface inspection.The key to its application is to plan high quality inspection trajectory,so that the surface information can be obtained as efficiently as possible while meeting the measurement requirements.Although many strategies have emerged for five-axis inspection trajectory planning,the trajectories generated by these algorithms are all reciprocating type.To form such reciprocating trajectory,the stylus tip must oscillate rapidly back and forth on the surface,which requires frequent acceleration and deceleration of the rotary axis and switching of the rotation direction.The dynamic performance of machine will decrease due to the sudden changes of force on the rotating axis,which will affect the inspection accuracy and efficiency.According to the above shortcomings,a trochoidal five-axis inspection trajectory planning algorithm is proposed in this thesis,which mainly includes two parts:(1)Planning the probe trajectory to determine surface measurement area and sequence.In this thesis,the first probe trajectory and its sub-regions are initialized using the tubular sweep surface method,and the first optimal probe trajectory is solved using the interference-free and contact angle conditions as constraints.The probe trajectory and partitions are extended in the same way until the surface is completely covered,and if the generation of the last probe trajectory produces an overlapping region,the region will be uniformly distributed and the corresponding probe trajectory is optimized by biasing.(2)Planning the sweep path to determine the scanning form of the stylus tips.Define the Trochoidal Scan Circle with a given step according to the optimal probe trajectory curve,and iteratively solve the optimal trochoidal step using the sampling chord error threshold as a constraint.Then extend the Trochoidal Scan Circle for each optimal step along the probe trajectory until the corresponding sub-region is completely covered by the Scan Circle,and smoothly connect them in turn to form a continuous trochoidal scan trajectory.Finally,through experimental comparison with various measurement methods,it is found that the proposed trochoidal scanning does not require reciprocal oscillation of the stylus during the inspection process,and can effectively avoid sudden changes in rotation direction,velocity acceleration,and force on the C-axis.The experimental results also show that the average sweeping efficiency of the trochoidal method can be increased by up to 68%compared to other methods,while the index which characterises the dynamic load of the machine,can be reduced by up to 95.14%.The above demonstrates that the method described in this thesis can simultaneously improve the dynamic performance and inspection efficiency. |
