Abstract: Aiming at the problem that position error of the target feature was affected by the real contact surfaces in different assembly modes, the relationship between the assembly position of geometric feature with the assembly error and geometric error of the assembling part was studied, and the automatic calculation method of the position error of the geometric feature based on the real machine model was proposed. Firstly, the combination of part assembly method and contact geometry type was summarized under the premise that the assembly contact surface was limited to the most common plane and cylindrical surface. Then, the control point variation model of real parts was introduced, and the algorithms for calculating assembly position of geometric features on the machine model, based on the various combination schemes of the assembly datum and the real assembly contact relationship, were established. Finally, the software for the real assembly position calculation was programed based on the Monte Carlo simulation, the sensitivity list and contribution rate list of all tolerance factors in the machine model and the probability distribution of the real position relative to the ideal position for the target feature were obtained. The experiment results show that the real position calculation method proposed for the assembly type, where the first datum is plane-to-plane bonding and the second and third datum are plane-cylinder surface contact, is correct.

Key words: assembly scheme; assembly tolerance analysis; control point variation model(CPVM); assembly position calculation