Fast evaluation of the volumetric motion accuracy of multi-axis machine tools using a Double-Ballbar

The proof of manufacturing accuracy requires continuous verification and crosscheck of the motion accuracy of machine tools. Machining in 5 to 6 axes intensifies the problem of measurement and evaluation of volumetric motion accuracy in up to 6 degrees of freedom (DOF) in the whole workspace. Although, there are many known, even standardized, measuring methods, they are either expensive, time-consuming, not applicable in an operational state of the machine under shop floor conditions, or their significance is limited to only 1 or 2 feed-axes. Appropriate methods to be run regularly, fast and cost-efficient by the machine operator as a performance test are still desired. The article presents a new approach that meets these requirements. It is based on a Double-Ballbar (DBB) with enlarged measuring range and volumetric measuring paths of up to 6 DOF with all feed-axes moving simultaneously during continuous measurement, instead of plane circular paths according to ISO 230-4. After an explanation of the proposed method, the developed DBB device is introduced, including its mechanical and sensor design, the data interface, and results of experimental investigations on the measuring accuracy. Furthermore, relevant problems regarding the design, optimization, and programming of appropriate 6 DOF measuring paths are discussed and experimental results are presented that show the advantage compared to other measuring paths.