Real-time Error Compensation System Research Articles

Multivariate orthogonal polynomial-based positioning error modeling and active compensation of dual-driven feed system

The nonsynchronous error of the dual-driven feed system seriously affects the positioning and machining accuracy of CNC machine tools. Improving the positioning error is an extremely important task as it determines the geometric accuracy of the manufactured parts. In this paper, a Multivariate Orthogonal Polynomial Regression model has been developed to predict the positioning error in terms of motion parameters such as position and speed of the X1 and X2 axes of the dual-driven worktable. Orthogonal Experimental Design has been engaged in conducting experiments. The positioning errors are measured by a dual-frequency laser interferometer. In addition, a real-time error compensation system is developed based on the proposed active compensation control strategy in the dual-driven feed system controlled by Beckhoff motion control card. Experimental results show that the proposed positioning error model and error compensation strategy can be utilized as an effective manner to improve the accuracy of dual-driven CNC machine tools.

Time-varying positioning error modeling and compensation for ball screw systems based on simulation and experimental analysis

Thermal expansion of ball screw systems affects the machining accuracy of machine tools significantly. This paper intends to provide a comprehensive error compensation method for the time-varying positioning error of machine tools. To confirm the thermal deformation mechanism of ball screw systems, experiments have been designed to study the thermal behaviors of a ball screw system under varying temperature conditions. An exponential algorithm is proposed to predict the temperature variation pattern of the ball screw based on finite element analysis, and the actual thermal boundary conditions of the ball screw system are exactly defined according to the proposed algorithm and the experimental results. Then, a comprehensive compensation model is established based on the decomposition of the initial geometric error and thermal error components. Finally, a real-time error compensation system is developed for machine tools based on the function of external machine original coordinate shift and fast Ethernet data interaction, and satisfactory results have been achieved for the compensation experiments on a machining center.

Research on the Thermal Deformation Pseudo-lag and Real-time Compensation for CNC Machine Tool Spindle

In order to study the thermal deformation law and to realize the real-time compensation for CNC machine tools, the theoretical and experimental analysis for CNC machine tool spindle thermal deformation are carried out. Results show that the relationship between the spindle thermal deformation and the spindle temperature is approximate linear relationship at about 1/3 distance away from the heat sources. That is to say, the spindle thermal deformation exist pseudo-lag. This conclusion provides a theoretical basis for temperature sensor setup and thermal error robust modeling. To verify the thermal deformation pseudo-lag, the spindle thermal errors of a VM850 machining center is measured, and the thermal error model is established according to the least square method. The spindle thermal deformation is compensated using the real-time error compensation system. The spindle thermal error is reduced by 90% compared with no compensation, and the spindle accuracy is greatly improved.

Geometric and thermal error compensation for CNC milling machines based on Newton interpolation method

The fast and accurate modeling for machine errors is an important step for the implementation of error compensation. In this article, a new approach for real-time compensation of geometric and thermal errors is presented, including an accurate error model and a real-time error compensation system. An experiment is carried out on a three-axis milling center to obtain machine positioning errors under different temperatures. A serial of error data collected under normal temperature is regarded as the basic error and modeled with the machine position coordinates based on Newton interpolation method which is also used for modeling the other error curves under different working temperatures in order to get their coefficients of fitting formulas. According to the relationship among these formulas, all the coefficients and the corresponding temperature variations are modeled using the Newton interpolation method again. The final compensation model can be obtained by substituting the coefficients of basic error formula. In addition, an external real-time error compensation system is developed based on the function of external machine zero point shift in Fanuc CNC systems. Experimental results show that the proposed geometric and thermal error compensation system can be utilized as an effective manner to improve the accuracy of CNC milling machines.

Modeling and Real-Time Compensation of Cutting Force-Induced Errors on NC Turning Center

This paper systematically presents the relationship between cutting forced-induced errors and the spindle motor current basing on kinematic chain of NC machine tools. Constructs the model of cutting force-induced errors with BP Neural network, and develops the real-time error compensation system. The compensation effect of this system is verified through the experiment and the compensation system is of a great importance to precision manufacturing industry.

Real-time cutting force induced error compensation on a turning center

Abstract A real-time error compensation system has been developed to reduce the cutting force induced planar error of a two-axis turning center by using sensing, metrology, modeling, and computer control techniques. Ten error components are formulated as a two-dimensional error field. A piezoelectric force sensor mounted in the pocket under the tool turret is used to characterize the cutting forces. A compensation controller based on an IBM/PC has been linked with the existing computer numerical controller (CNC) to correct machine errors in real time. Three different types of cutting tests were performed and the results showed that the maximum diameter error in the workpiece was reduced by 67–85% using this compensation system.

The real-time error compensation technique for CNC machining systems

One of the important trends in precision machining is the development of real-time error compensation technique. This paper presents the research work under the authors and their team in this area. The technique has been applied to more than 10 different kinds of machines including: turning centers and machining centers; small, medium and large machines; new products and retrofitted machines. The accuracy improvement is in the range of 3–10 times. The error sources being compensated for include machine geometric and thermal errors, cutting force-induced errors, and workpiece thermal errors. The paper discusses some important aspects of the technique: the general approach for developing real-time error compensation system; the formulation of the error synthesis model; the mapping of the machine errors; optimal modeling; thermal error mode analysis; the optimization of the sensor locations; cutting force-induced error compensation; compensation control implementation; and other critical problems in the real-time error compensation technique.

Real-time cutting force induced error compensation on a turning center

A real-time error compensation system has been developed to reduce the cutting force induced planar error of a two-axis turning center by using sensing, metrology, modeling, and computer control techniques. Ten error components are formulated as a two-dimensional error field. A piezoelectric force sensor mounted in the pocket under the tool turret is used to characterize the cutting forces. A compensation controller based on an IBM/PC has been linked with the existing computer numerical controller (CNC) to correct machine errors in real time. Three different types of cutting tests were performed and the results showed that the maximum diameter error in the workpiece was reduced by 67–85% using this compensation system.

Integrated real time compensation system for errors introduced by measurement probe and machine geometry in commercial CMMs

In this paper, an integrated real time compensation system has been proposed for the errors introduced by the probe and machine geometry in commercial CMMS. For efficient probe error mapping, a compact notation (ϵ, θ) for probing direction and corresponding concentric diagram is proposed. A set of integrated volumetric error equations are also proposed for the volumetric error map integrating the probe error and the machine geometric error. For the real time error compensation scheme, an interface box and an appropriate software driver have been designed and implemented between the CMM and machine controller. The data flow is intercepted and corrected according to the integrated volumetric error map without the controller being noticed. Thus the real time error compensation system has been successfully implemented for the machine with minimum interference to the existing coordinate measurement system. The developed system has been applied to a commercial CMM on the shop floor, and the measurement accuracy has been improved remarkably.

Accuracy enhancement of a horizontal machining center by real-time error compensation

A real-time error compensation system was developed to improve the geometric-thermal volumetric accuracy of a T-10 machining center by using sensing, metrology, modeling, and computer control techniques. Including thermal errors, 32 error components are formulated as a four-dimensional error field in the time-space domain. Fifteen thermal sensors are used to characterize the temperature field of the machine. A compensation controller based on the IBM/PC has been linked with an Acramatic-950 CNC controller to compensate for machine errors in real time. The maximum linear displacement error in four body diagonals was reduced from 140 μm to 34.5 μm with this compensation system, and the spindle thermal drift in space was reduced from 147.3 μm to 16.8 μm.