Implementation Study Of Machine Tool Error Compensation Based On FANUC And SIEMENS840D CNC Systems

Applying error compensation technique of NC machine tools topractical production is a key subject in the field of precision machining. Thispaper focused on error compensation implementation of machine tools withFANUC or SIEMNES840D CNC system, systematically investigated errorcompensation functions of the two systems, realized real-time datainteraction between an error compensator and the CNC systems, proposednew methods of machine-tool error measurement and modelling, and usedactual processing cases to verify the feasibility and efficiency of thetheoretical work. What’s been done can be concluded as follows:(1) Investigated the characteristics and limitations of error compensationfunctions of the two CNC systems, including leadscrew error compensation,backlash compensation, temperature compensation, etc, and put forwardconcrete implementation methods about them. (2) Explored data interaction approaches between an error compensatorand the two systems. Two kinds of communication solutions—by I/O portsand by network, were put forward to effectively match different FANUCsystems. As for SIEMENS840D systems, secondary development with VBsoftware were conducted. A read-write data platform was established on theCNC system interface, and compensation values and coordinate values couldbe transmitted by R parameters to enable real-time error compensation.(3) New methods of machine-tool error measurement and modellingwere proposed, taking guideway straightness error and spindle thermal erroras example. The former was investigated by way of machining workpieces.Based on guideway straightness errors of a machine tool and a workpiece byan Agilent laser interferometer, a hybrid modeling method was proposed toadapt to the batch-production requirement. In view of the pseudo-hysteresiseffect of machine tool thermal error, a thermal error modeling method basedon a state-space model was proposed, taking temperature of the key heatsources as its input and thermal error as its output. History information iscontained in the state variable. Its parameters could be obtained by subspaceidentification algorithms. Then, experiments on a lathe revealed this thermalerror model could predicted70%of the error and demonstrated strongrobustness. (4) Application of error compensators in factories was introduced.Compensation test of workpieces showed guideway straightness errors of alarge gantry machine with FANUC31i system were reduced by60%. Also,for a turning-milling machining center with840D system, the thermal errorof its spindle dropped from40μm to9μm after compensation.