由于并联机构铰链间隙的存在，使并联机构的实际精度和刚性明显减小。本文论述了采用冗余驱动技术改善并联机构精度的研究。首先分析了可以将铰链间隙对并联机构运动误差的影响转化为杆长偏差对机构误差的影响，然后通过分析得出：由于铰链间隙的影响，并联机构运动空间是空间几个球环的交集，采用数值法，利用球坐标积分求出误差空间的体积大小，最后对具有相同结构参数的非冗余和具有冗余驱动的两种并联机构，在同样的工作空间内分别计算了误差分布，得出采用冗余驱动技术可以有效减小因铰链间隙而引起的并联机构运动误差的结论。

CAD/CAM systems provide the possibility to integrate with NC post-processors, so the NC program can directly execute post-processing in a CAM system. But surveys taken by CAM users indicated that producing a formatted NC program remained to be one of their most perplexing problems. In this paper, based on the general introduction of the NC post-processing, the authors discussed the important roles of post-processing in NC modules, and analyzed some problems in popular post-processors integrated with CAM system. This paper also recommended some famous post-processing products and their features. At last some suggestions and a sample post-processing of parallel machine were given to solve the problems.

Correlative error is a kind of error between the cutter locations. This text presents a detailed analysis about correlative error in the principal axis method (PAM) that is a strategy of tool positioning for five-axis machining. It points out all the strategies based on linear projection can not avoid this interference and cannot be disregarded especially in the strategies with large stepover. Accurate calculating is made individually on linear and curve feed and formulae are developed. The author also gave the available application range of PAM and the algorithm for estimating correlative error.