Abstract: The marking of the hole group position degree on the part sometimes appears without a reference, which is in accordance with the requirements of GB/T, but often causes disagreement between the measurer and the designer, resulting in less accurate evaluation. In this paper, a theoretical calculation model of hole group position degree is given based on the least squares method, and then a mounting bracket is used as an example to carry out the actual measurement and evaluation with a CMM, and the results are compared with those of PC-DMIS software to verify the validity of this datum-free hole group position degree measurement and evaluation model.

Key words: CMM; Position degree; Least squares method; Hole group without datum; Measurement model

摘要： 零件上孔组位置度的标注有时会出现无基准的情况，这虽然符合国标的要求，但却往 往引起测量人员与设计人员之间的分歧，导致评价不够准确。文章在最小二乘法的基础上， 给出了一种孔组位置度的理论计算模型，然后以某安装支架为例，用三坐标测量机进行了实 际的测量和评价，并与 PC-DMIS 软件的结果进行了对比，验证了该种无基准孔组位置度测量 评价模型的有效性。

关键词: 三坐标测量；位置度；最小二乘法；无基准的孔组；测量模型