Research On Error Modeling And Compensation For Heavy-duty CNC Floor-typed Boring And Milling Machine Tool

With the continual development of science and technology, the demands forproducts’ precision are higher and higher in various fields. As a result of their largestructures and movement ranges, heavy-duty CNC machine tools’ geometric errorsare obvious; and due to their weighty mass and higher driving power, they willgenerate much heat, consequently their thermal induced errors is also prominent.Error compensation technologies are concernful means of improving machinetools’ precision. In this thesis, existing error compensation technologies researchstatus were analyzed firstly, then combining Major National S&T Program andmanufacturing enterprises’ requirements, for example ram thermal elongation erroris obvious and so on, aiming at the problems when error compensation technologyis implemented for heavy-duty CNC machine tools, the error compensationtechnology of heavy-duty CNC floor-typed boring and milling machine tools,which includes error modeling, error measurement, error identification and errorcompensation implementation, was researched.Error modeling is one of key technologies in error compensation field.Conformal geometric algebra theory was attempted to apply in the error modelingtechnology field, and a new error modeling method which was based on conformalgeometric algebra was proposed in this thesis. Firstly, rotations and translations ofrigid body movement was expressed as a uniform formula with the geometricproduct of conformal geometric algebra; then, components of errors in3-axesmachine tools were classified into translation components and rotation components;and the movement of adjacent bodies in multi-body system were researched. Idealmovement in which error movements wasn’t calculated and actual movements inwhich error movements was calculated were researched and modeled withconformal geometric algebra theory; and then the machine tool’s error model wasconstructed according to the tip of tool is the same with the point which is cuttingin the workpiece. Finally, take a heavy-duty CNC floor-typed boring and millingmachine tool as an example, error model based on conformal geometric algebrawas obtained and the precisions of the error model were researched.To obtain the characteristic of machine tools’ error, error measurement anderror identification are needed firstly before error compensation are implemented.Researching the problems on measuring small errors in large movement ranges, anew measurement and identification method for heavy-duty CNC machine tools’large movement ranges was proposed, which was finished by measuring volumeerrors with a laser tracker firstly, then components of the errors were identified based on conformal geometric algebra model. Basing on the analyzing of themeasurement error for the laser tracker, the error identification principle wasproposed. Finally, geometric errors in a heavy-duty CNC floor-typed boring andmilling machine tool were measured and identified, and the mathematic models ofgeometric error components were constructed through least square polynomialfitting method.Thermal errors are the main of heavy-duty CNC machine tools’ volume errors,and an on-line measuring and compensating system was proposed for the ramthermal elongation error firstly in this thesis. Temperature sensors mounted on theram were not required in this system which can be used in various operatingconditions. An invar pole whose thermal expand coefficient is near to zero wasused as a benchmark, and a displacement sensor, which could obtain ram’selongation value and sent it to CNC system, was installed in one end of invar pole.Then, a new thermal error modeling method was proposed. Firstly, suitabletemperature sensors were mounted on the machine tool, and thermal error weremeasured with a laser tracker, then to get thermal error parameters, thermal errorsobtained from the experiments were separated from geometric errors. At the sametime, basing on temperature sensors optimizing distribution strategies, key pointsof thermal errors were selected. Finally, a multiple linear regression model wasconstructed.The implementation strategy of error compensation is another key technology.Basing on handwheel offset function of CNC system, a novel error compensationimplementing strategy were proposed, and an error compensator was developed torealize the error compensation implementing on machine tools with Siemens840DCNC systems, which communicates with CNC system by the handwheel offsetfunction and substitutes for electronic handwheel of CNC system. The errorcompensator’s hardware and software systems, in which coordinates positionsacquiring, temperature collecting and third handwheel application in Sinumerik840D were included, were researched. And multithread technique was used toparallel run to avoid CPU’s long-playing employment by one task, were developed.Error model validation and compensation experiments on a heavy-duty CNCfloor-typed boring and milling machine tool were designed, which laid afoundation for applying error compensation technology in the industries.