A parallel machining robot and its control method for high-performance machining of curved parts

The curved part with open-and-close angle conversion features is a kind of well-known difficult-to-machine part. Using traditional five-axis serial machine tools (SMTs) may cause efficiency and accuracy reduction at open-and -close angle conversion regions because of the singular points in their orientation workspace. How to achieve high-efficiency and high-precision machining of this kind of curved part is a challenging issue in the field. In order to solve this problem, a parallel machining robot (PMR) with five degrees of freedom (DoFs) is developed. Accordingly, the attitude coupling adjustment mechanism of the developed PMR is disclosed, which indicated that a small change of the tool orientation will never lead to a large range motion of the driving limbs. Thus the robot has the potential to pass through open-and-close angle conversion regions smoothly. In order to take full use of the advantages of the developed PMR in attitude adjustment, a control method is proposed by fitting tool orientation spline in unit spherical coordinate system. On this basis, toolpath planning and machining experi-ments are carried out to verify the performance of the developed PMR and the proposed control method when machining parts with open-and-close angle conversion features. Experimental results demonstrate that the developed machining robot integrated with the proposed control method can improve the machining efficiency and accuracy significantly when compared with the SMT. This proves that the attitude coupling motion property of PMRs can solve the difficulty in high-performance machining of open-and-close angle conversion features. The findings of this study fundamentally provide a feasible way to overcome the abnormal phenomena when machining curved parts with open-and-close angle conversion features.