A Novel Double-Ball-Bar with Two Spatial Linkages and One Spherical Joint

As a typical comprehensive error measurement method, the double-ball-bar (DBB) has been invented and used widely for evaluating and diagnosing the accuracy of NC machine tools. However, due to the expansion length of DBB's bar is very limited, the working efficiency of the DBB is greatly reduced and different length bars are mostly used to realize different measurement ranges. In this paper, a novel DBB with two spatial linkages and one spherical joint was presented to implement a wide detection range and simplify the operation. The structure of the proposed device was firstly introduced. The working principle of the device was then described, and the mathematical model for detecting machine's accuracy was also built. According to the angle of spatial linkages and lengths of two bars, circular motions trajectory which is caused by interpolation movement of two shafts can be calculated and compared with theoretical value to evaluate machine tool's accuracy. Finally, the simulation was done to validate the feasibility of the proposed device. The results show that the proposed DBB has reasonable structures. Moreover, the measuring range can cover a large region of space and it is continuous.