The positional deviation in two axes

Abstract

The positional deviation (difference between the actual and target position) belongs to the important criteria that describe the performance of numerically controlled axes. The procedure for determination of such deviation is described in the international standard ISO 230-2:1997. This standard provides calculation of the positional deviation only in several discrete (measuring) points. Moreover it does not consider effects of the measuring instrument on the obtained results. The new methodology is adopted and it is enables estimation of the positional deviation in any point of the axis travel, together with the uncertainty of such estimate. Obtained results can be incorporated into a control system in the form of corrections enhancing positioning possibilities of individual axes. The paper introduces procedures that were verified by measurements for one linear axis. The more complicated situation occurs for testing the positioning accuracy in a plane or in a space respectively. Therefore possible solutions for determination the repeated positioning accuracy in any point of the plane are presented at the end of the paper, together with expression of the respective uncertainty.