Analysis of the optimal orientation of robot gripper for an improved capability assembly process

The objective of the article is to increase the probability of achieving a joint of cylindrical machine parts, through appropriate orientation of the robot gripper of the assembly robot, while ensuring the best parameters of the assembly process and the required process capability, without unnecessarily increasing the accuracy of the assembly workstation equipment. The presented methodology for the summation of errors, besides its simplicity, has an additional advantage compared with the method of the summation of variance or error vectors separately in regard to each axis of the adopted coordinate system, because it takes into account the nature of the relationships between variables (covariance). The analysis showed that by rotation of the gripper around an oriented axis of the machine cylindrical part, the probability of the joint and process capability index Cp value can be increased from Cp= 1.17 to Cp=1.33. The optimal orientation of the robot gripper enables the clearance fit between mating parts to be reduced by 8% and 19% with respect to its extreme unfavourable setting. However, this setting of the robot gripper reduces the sensitivity of the system to the effects of systematic errors.