Abstract
Due to the errors of the servo system and the errors of the ball screw drive system, the positioning errors inevitably occur in the process of CNC machine tools. The measurement of traditional equipment is limited by a fixed measurement radius and a single degree of freedom, which can only be measured within a fixed plane. In this paper, four different positioning errors of CNC machine tools are first measured at full scale by using J-DBB (a modified double ball bar with one spherical joint connecting two bars) method. The J-DBB device uses a three-degree-of-freedom spherical joint as a connecting part, which realizes that the measurement radius can be continuously changed, and the measurement space is a spatial sphere. First, the principle of the J-DBB method is briefly introduced. Next, four typical positioning errors of CNC machine tools are analyzed and examined, which contain the uniform contraction error of ball screw and linear grating, periodic error of the ball screw and linear grating, interference of measurement devices error, and opposite clearance error. In the end, the trajectories of the CNC machine tool spindle with a single positioning error are simulated by using the J-DBB method. The results reveal that this method can be used for the positioning error of machine tools, which helps to better understand the spatial distribution of CNC machine tool errors and provides guidance for the reasonable selection of working areas to improve the machining accuracy of parts.
Highlights
Machining parts with high accuracy is a key issue in the field of precision manufacturing
When the second ball moves with the CNC machine tool spindle, the motion is diaxis of swing vided into the rotary movement of the two mechanical decoupling frames (MDF)
This paper proposes a J-Double ball bar (DBB) method that combines the structural characteristics of traditional DBB and two-bar linkage DBB
Summary
Machining parts with high accuracy is a key issue in the field of precision manufacturing. A measurement technique based on telescopic DBB is proposed to measure the thermal error of CNC machine tools [14]. Many new devices based on the DBB method were designed to better measure the error of machine tools. A linkage bar mechanism composed of rotary encoder was proposed to improve the measurement accuracy of machine tool motion error [20,21]. This new device with a variably measuring radius can largely extend the measurement ranges. This paper measured the positioning errors of the CNC machine tool at full scale using the J-DBB method.
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