Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
4,845
result(s) for
"error compensation"
Sort by:
Event-triggered predefined-time control for full-state constrained nonlinear systems: A novel command filtering error compensation method
In this paper, a command filter-based adaptive fuzzy predefined-time event-triggered tracking control problem is investigated for uncertain nonlinear systems with time-varying full-state constraints. By designing a sliding mode differentiator, the inherent computational complexity problem within the predefined-time backstepping framework is solved. Different from the existing command filter-based finite-time and fixed-time control strategies that the convergence time of the filtering error is adjusted through the system initial value or numerous parameters, a novel command filtering error compensation method is presented, which tunes one control parameter to make the filtering error converge in the predefined time, thereby reducing the complexity of design and analysis of processing the filtering error. Then, an improved event-triggered mechanism (ETM) that builds upon the switching threshold strategy, in which an inverse cotangent function is designed to replace the residual term of the ETM, is proposed to gradually release the controller’s dependence on the residual term with increasing time. Furthermore, a tan-type nonlinear mapping technique is applied to tackle the time-varying full-state constraints problem. By the predefined-time stability theory, all signals in the uncertain nonlinear systems exhibit predefined-time stability. Finally, the feasibility of the proposed algorithm is substantiated through two simulation results.
Journal Article
Thermal error compensation of high-speed spindle system based on a modified BP neural network
The accuracy, convergence performance, and robustness of the thermal error model based on traditional artificial neural networks (ANNs) are poor because the model is sensitive to the training data. To improve these performances, the genetic algorithm (GA) and particle swarm optimization (PSO) were used to optimize the parameters of ANNs with back propagation (BP) algorithm, such as the number of neurons in the hidden layer, initial weights, and thresholds. Moreover, the fuzzy cluster grouping and correlation analysis were combined to group and optimize the typical temperature variables to guarantee the robustness of the thermal error models based on BP, GA-BP, and PSO-BP neural networks. Then, thermal error compensation experiments were conducted on the spindle system of a precision jig borer, and the machining accuracy was increased from 67 to 78 % for the GA-BP model and 89 % for the PSO-BP model, respectively. To validate the effectiveness of the thermal error measurement, modeling, and compensation methods, the test samples were machined and the surface quality of the machined parts was measured. By measuring the dimension error and the surface quality of the machined parts, the results showed that the machining error can be reduced and that the surface quality can be improved by the thermal error compensation. Moreover, the accuracy, convergence performance, and robustness of the thermal error model based on the traditional BP neural network can be improved greatly by GA and PSO.
Journal Article
Optimal deformation error compensation process in flank milling of thin-walled workpieces
In order to reduce static deformation and improve machining accuracy, deformation error compensation by offline adjustment of machining parameters is a practical approach in the flank milling process of thin-walled workpieces. Since machining parameters are coupled with cutting force and deformation, iterative methods are required for error compensation. However, current error compensation models lack an in-depth understanding of the compensation process, resulting in low convergence rate of the compensation process. To overcome these problems, a double flexible error compensation model (DFCM) for deformation is proposed in this paper. As the basis of the proposed model, iterations of machining parameters in error compensation are first introduced. After that, the deficiencies of the flexible error compensation model (FCM) for deformation are revealed, and the reasons for its large iteration space and low convergence rate are given. Then, the DFCM is developed from the flexible iteration process of machining parameters and the FCM. The proposed DFCM reveals the actual error compensation process and has significant advantages over the FCM; thus, it converges with the faster rate. Finally, effectiveness and advantages of the DFCM are verified by simulations and experiments of flank milling of thin-walled workpieces.
Journal Article
Volumetric error compensation of machine tool using laser tracer and machining verification
Volumetric error is a primary factor that affects the accuracy of machining tools. The ability to ascertain volumetric error in a rapid and simple manner is of significant importance, and this can remarkably reduce the probability of temperature variation during the experiment. This study proposes a strategy for volumetric error measurement and compensation based on laser tracer for the 3-axis numerical control (NC) machining tool, and verifies the machining accuracy of a concave semi-spheroid test piece. In this study, the calibration methods employed by the laser tracer and the error separation algorithm of the machining tool are initially investigated. Following this, the accuracy of the geometric error measurement is verified using the laser interferometer. The cubic spline interpolation method is then employed to establish the tool path volumetric error model in the 3-axis NC machining tool, and the G-code modification is conducted for volumetric error compensation. Experiment results show that when the error compensation is performed, the improvement in the accuracy as compared with the initial state exceeds 50% not involving machining. To evaluate the accuracy and effectiveness of the proposed method, two machining tests to obtain a concave semi-spheroid test piece with and without volumetric error compensation strategy are studied, and the corresponding accuracies are measured by a high precision coordinate–measuring machine. It is found that the machining accuracy after having performed the error compensation is approximately 43% higher than that obtained on the pre-volumetric error compensation.
Journal Article
Spindle unit thermal error modeling and compensation based on digital twin
The thermal error in the spindle unit is substantial and necessitates mitigation. Current models, being predominantly static in nature, have limited efficacy in error control. Integrating digital twin technology for modeling and controlling spindle unit thermal error holds promise in enhancing the machining accuracy of machine tools. Yet, the notion of a digital twin system specifically tailored for spindle unit thermal characteristics remains uncharted territory. To navigate these challenges, this study introduces a novel digital twin system tailored for spindle unit thermal characteristics. This system is poised to revolutionize thermal error modeling and compensation by harnessing the capabilities of digital twin technology. Within this digital twin framework, both the thermal error control model and the analytical thermal characteristic model are seamlessly integrated. The control model is devised as an exponential function, utilizing operational time, inherent time constants, and both initial and equilibrium thermal errors as parameters. Delving deeper, the analytical thermal characteristic model for the spindle system is rooted in a thermal resistance network approach. This leads to a closed-loop thermal characteristic modeling process, culminating in the derivation of a steady-state thermal error. Intricate heat transfer dynamics between spindle components are dissected, and a comprehensive thermal equilibrium equation set is formulated for the spindle unit. This equation set comprehensively accounts for dynamic variations in key parameters such as preload, lubricant viscosity, thermal load intensity, thermal contact resistance, and convective coefficients. To ascertain the time constant, a meticulously designed set of thermal characteristic experiments is executed. Subsequently, the digital twin system embarks on predictive modeling of thermal errors across varied operational conditions. This prediction then forms the foundation for thermal error compensation. With the integration of the present model into the digital twin system, the results are impressive: the absolute average and maximum deviations in thermal elongation, post-error control, stand at approximately 0.40 μm and 1.24 μm, respectively.
Journal Article
Study of the Operational Safety of a Vascular Interventional Surgical Robotic System
This paper proposes an operation safety early warning system based on LabView (2014, National Instruments Corporation, Austin, TX, USA) for vascular interventional surgery (VIS) robotic system. The system not only provides intuitive visual feedback information for the surgeon, but also has a safety early warning function. It is well known that blood vessels differ in their ability to withstand stress in different age groups, therefore, the operation safety early warning system based on LabView has a vascular safety threshold function that changes in real-time, which can be oriented to different age groups of patients and a broader applicable scope. In addition, the tracing performance of the slave manipulator to the master manipulator is also an important index for operation safety. Therefore, we also transformed the slave manipulator and integrated the displacement error compensation algorithm in order to improve the tracking ability of the slave manipulator to the master manipulator and reduce master–slave tracking errors. We performed experiments “in vitro” to validate the proposed system. According to previous studies, 0.12 N is the maximum force when the blood vessel wall has been penetrated. Experimental results showed that the proposed operation safety early warning system based on LabView combined with operating force feedback can effectively avoid excessive collisions between the surgical catheter and vessel wall to avoid vascular puncture. The force feedback error of the proposed system is maintained between ±20 mN, which is within the allowable safety range and meets our design requirements. Therefore, the proposed system can ensure the safety of surgery.
Journal Article
A novel method of volumetric error compensation for aspherical grinding machine considering error coupling effect and compensation strategy
Aspheric surface grinding is a critical process for processing large aspheric components, where the precision and surface quality directly influence the efficiency of the entire machining process. In this process, the comprehensive volumetric error of the machine tool significantly impacts the precision of the workpiece’s shape. This paper first examines the mechanism of volumetric error transmission in optical plane grinding machine, and utilizing screw theory and incorporating the machine tool’s topological structure, we derived a volumetric error model suitable for XYZ three-axis machine tools. Additionally, this study elucidated the impact of Abbe error on the machine’s spatial precision and revised the model based on the Abbe principle. The model’s effectiveness was validated by measuring the body diagonal error of the machine. Lastly, we proposed an advanced optimization strategy for machining point positions based on the genetic adaptive particle swarm optimization (GA-APSO) algorithm. Further, based on the theory of arc enveloping grinding and the established volumetric error model of the machine tool, we developed specialized computer-aided manufacturing (CAM) software suitable for aspheric surface grinding and conducted aspheric surface machining test. The results show that the optimized screw theory model can compensate the machine tool volumetric error to about 6 µm, increasing the compensation rate from 60% before the correction to 81% after the correction, and reducing the PV value of a 200-mm diameter aspherical surface from 14.8 to 9.2 µm, effectively improving the machining accuracy.
Journal Article
Real-time estimate and control contour errors for five-axis local smoothed toolpaths based on airthoid splines
Five-axis linear commands are blended as the local smoothed toolpaths by inserting clothoid and airthoid splines at corners in five-axis CNC machining. The contour error is the bottleneck to achieve the precise dimension of the machined parts, when following the local smoothed toolpaths. This paper presents a contour error estimation and control method for the five-axis smoothed toolpaths with airthoid splines, according to the geometric characteristics of the toolpaths. The tool-tip contour error is analytically calculated based on the expression of the smoothed toolpaths. Consequently, the tool-orientation contour error is obtained by synchronizing the tool-orientation contour point with the tool-tip item based on the motion time through the designed time scale coefficient, when the toolpaths are scheduled by the time-synchronization scheme. Furthermore, a contour error compensation strategy is constructed to adaptively determine the compensator gain. It can be qualified to maximally eliminate the contour errors and steadily hold the control stability of the feed drives, in spite of the modeling error between the nominal and actual control models. The simulation and experiment results show that the estimation algorithm has higher accuracy than traditional methods, and the compensation strategy effectively eliminates the five-axis contour error.
Journal Article
A novel feedrate scheduling method using modifying S-shaped feedrate profile with a round-off error elimination approach for CNC machining
Round-off error is inevitable in computer numerical control (CNC) systems because it is challenging to ensure that the interpolation time is an integer multiple of the interpolation period. This error can affect both machining precision and motion smoothness. To eliminate the round-off error and improve machining speed and precision, a novel round-off error elimination method is proposed that modifies the S-shaped acceleration/deceleration (ACC/DEC) feedrate scheme. Firstly, an adapted bidirectional scanning algorithm is applied to a jerk-limited S-shaped feedrate profile to improve machining efficiency while respecting feedrate constraints. Secondly, during the interpolation stage, the velocity round-off error is first introduced. Based on the novel properties of the modified S-shaped scheme, the displacement round-off error is then analyzed and addressed using different strategies, such as modifying the S-shaped profile with one-cycle rounding-up in a specified section or segment transition, without crossing the end point. Finally, a series of simulation and real machining experiments are conducted to compare the proposed method with existing round-off error compensation algorithms. The results show that the proposed method offers more flexible and effective round-off error compensation, with significant improvements in machining efficiency and the smoothness of the motion profile, including velocity, acceleration, and jerk. The real machining experiments, conducted in a CNC system with a 250-µs real-time control period and focused on 3D complex surface engraving, verified the practicality of the proposed method.
Journal Article