基于误差转换的汽车曲轴圆度及圆柱度误差评价数学模型构建研究

针对国内汽车曲轴轴颈圆度误差、圆柱度误差检测普遍存在的效率低、精度低等问题,建立基于误差转换的平面曲线和空间曲线误差数学模型,结合圆和圆柱的数学表达建立满足最小包容条件的圆度和圆柱度误差评定数学模型,并采用遗传优化算法计算出符合最小评定要求的曲轴轴颈形位误差,解决了理想包容要素位姿参数不精确的问题。同时,建立基于图像域的汽车曲轴轴颈形状误差检测试验台,针对测量过程中连杆轴颈沿主轴颈公转运动,从而导致连杆轴颈图像域检测数据存在坐标不归一问题,以曲轴法兰端特征孔为基准,通过模板匹配特征与孔边缘提取实现了连杆轴颈圆度和圆柱度测量数据空间坐标归一化处理。以某型号发动机曲轴为例进行大样本误差检测试验,并与三坐标测量机测得的结果进行对比,数据分析表明提出的曲轴轴颈形状误差检测方法的精度为1μm,且重复检测误差在0.1μm以内,证明了其理论上的正确性及实践操作的可行性。

Research on Automobile Crankshaft Roundness and Cylindricity Errors Evaluation Mathematical Model Based on the Error Conversion

Automobile crankshaft roundness error and cylindricity error detection is necessary, and there exists low efficiency, low accuracy presently. The tolerance evaluation model of plane curve and space curve is established based the error conversion principle. The roundness and cylindricity error evaluation mathematical model are also established according on the minimum zone method, the genetic algorithm is used to calculate the form and position errors of the crankshaft with minimum assessment requirement, the method solve the problem of ideal contain elements of the pose parameters being not accurate. Meanwhile the automatic detection scheme of automobile crankshaft shape error is designed based on image domain. The connecting rod shaft is revolute along the main shaft neck, so the measurement data in the image domain is not in the same coordinate system. In order to solve the problem, the holes in the crankshaft flange end are chose as datum feature and through template matching and the hole edge extraction, the rotation angle of the connecting rod shaft has gotten. A certain type of engine crankshaft as an example is taken to have the large number of error detection, and the measured results are compared with the results of the three coordinate measuring machine. Data show that the crankshaft shape error precision of the proposed detection method is 1 μm, and duplicate detection error less than 0.1 μm, so the this method is correct in theory and feasible in practice.