複数の面分からなる形体へ適用可能な幾何公差方式の提案

Abstract

For controlling geometric deviations of machine parts, the Japanese Industrial Standards define geometric tolerances. In geometric tolerancing, a feature of an actual part is acceptable if it can be contained within a spatial tolerance zone. Geometric tolerances in the standards are only defined for primitive planar and cylindrical features, therefore designers have difficulties in specifying a proper geometric tolerance to a surface feature with complex shape. An extended geometric tolerancing method is proposed in this paper which is applicable to a composite feature with several primitive faces. This method satisfies the "principle of independency" so that it can control geometric deviations of an actual surface feature regardless of its sizes. It is compatible to the current geometric tolerancing practice also. A concept of parameterized features is introduced to represent modifications of a composite surface feature according to its size variations. Features with the correct form, features in the correct orientation, and features in the correct position are defined by using a parameterized feature with variable sizes. A geometric tolerance is formalized as a spatial zone of acceptable deviations measured with respect to such a reference feature with the correct geometry.