According to the theory of spatial mechanics

CMM(Coordinate Measuring Machine)can be classified as two groups

that is the serial-mechanism CMM and the parallel-mechanism CMM. Generally

the parallel-mechanism CMM has higher measuring accuracy and more flexible probe posture than the serial-mechanism CMM. Secondly

the parallel-mechanism CMM is of high technical additional value because its ‘hardware' is simple and the ‘software' is complex. Therefore

theoretical and experimental research for this new kind of CMM has currently become a hot topic for both industry and academia. In this paper

the state-of-the-arts and the drawbacks of Cartesian CMM are discussed and the characteristics of the parallel-mechanism CMM are introduced. Then the theoretical base

the research situation and the trend about the parallel-mechanism CMM around the world are synthesized. Finally

the problems

which should be noticed in researching the new CMM

are discussed.