Fangyu Peng

A measurement strategy and an error-compensation model for the on-machine laser measurement of large-scale free-form surfaces

This study presents a novel measurement strategy and an error-compensation model for the measurement of large-scale free-form surfaces in on-machine laser measurement systems. To improve the measurement accuracy, the effects of the scan depth, surface roughness, incident angle and azimuth angle on the measurement results were investigated experimentally, and a practical measurement strategy considering the position and orientation of the sensor is presented. Also, a semi-quantitative model based on geometrical optics is proposed to compensate for the measurement error associated with the incident angle. The normal vector of the measurement point is determined using a cross-curve method from the acquired surface data. Then, the azimuth angle and incident angle are calculated to inform the measurement strategy and error-compensation model, respectively. The measurement strategy and error-compensation model are verified through the measurement of a large propeller blade on a heavy machine tool in a factory environment. The results demonstrate that the strategy and the model are effective in increasing the measurement accuracy.

Anisotropic force ellipsoid based multi-axis motion optimization of machine tools

The existing research of the motion optimization of multi-axis machine tools is mainly based on geometric and kinematic constraints, which aim at obtaining minimum-time trajectories and finding obstacle-free paths. In motion optimization, the stiffness characteristics of the whole machining system, including machine tool and cutter, are not considered. The paper presents a new method to establish a general stiffness model of multi-axis machining system. An analytical stiffness model is established by Jacobi and point transformation matrix method. Based on the stiffness model, feed-direction stiffness index is calculated by the intersection of force ellipsoid and the cutting feed direction at the cutter tip. The stiffness index can help analyze the stiffness performance of the whole machining system in the available workspace. Based on the analysis of the stiffness performance, multi-axis motion optimization along tool paths is accomplished by mixed programming using Matlab and Visual C++. The effectiveness of the motion optimization method is verified by the experimental research about the machining performance of a 7-axis 5-linkage machine tool. The proposed research showed that machining stability and production efficiency can be improved by multi-axis motion optimization based on the anisotropic force ellipsoid of the whole machining system.

Adaptive Notch Filter Control for the Torsion Vibration in Lead-Screw Feed Drive System Based on Neural Network

In the machining process, the nature vibration characteristics of feed drive frames are in time-varying. The nature frequencies of the torsion vibration in the lead-screw feed drives are notably changed with the table position, which further influences the stability of servo control. Building the model of servo drive system under consideration of torsion vibration of rotor-screw system, this paper analyzes the effect of changing torsion vibration modes on the notch filter control. The results display that the compensation using the conventional notch filter cannot suppress those disturbances induced by the time-varying vibration modes. Therefore, an adaptive notch filter control method is presented based on an improved BP neural network in this paper. A case study demonstrates that the parameters of the notch filter can be adjusted rightly according to the different table position. Consequently, the torsion vibration modes are compensated efficiently for the time-varying table positions.

A Method of General Stiffness Modeling for Multi-axis Machine Tool

In this paper, a new method for computing general stiffness model at tool tip for multi-axis machine tool is presented. The formula of general stiffness model at tool tip is derived from virtual-work principle and point transformation matrix method. Point transformation matrix method indicates the transformation relationship of elastic displacement on both ends of flexible axes as well as the transformation relationship of force. By multiplying the point transformation matrix, the final stiffness matrix at tool tip will be obtained efficiently. In this modeling method, the final stiffness matrix is composed of local compliance matrixes according to their contribution to the final stiffness matrix.

Look-Ahead Scheme for High Speed Consecutive Micro Line Interpolation Based on Dynamics of Machine Tool

This paper presents a new look-ahead Scheme with adaptability of dynamics of machine tool for high speed consecutive micro-line interpolation. A backtracking arithmetic is used to calculate the speeds in the link points of consecutive micro-lines. Moreover, the speed limitations in the link points are analyzed in detail and the compound constraint conditions of the motion axes is introduced based the dynamic characteristics of machine tool. The case studies indicate that, using the scheme presented by this paper, the actual interpolation speed is closer to the command speed and the shock that results from the sharp fluctuate of feed speed is depressed, which will improve the machining efficiency and quality.

Estimation of Cutter Deflection Based on Study of Cutting Force and Static Flexibility

In the tool orientation planning for five-axis sculptured surface machining, the geometrical constraints are usually considered. Actually, the effect of nongeometrical constraints on tool orientation planning is also important. This paper studied one nongeometrical constraint which was cutting force induced static deflection under different tool orientations, and proposed a cutter deflection model based on that. In the study of the cutting force, the undeformed chip thickness in filleted end milling was modeled by geometrical analysis and coordinate transformation of points at the cutting edge. In study of static flexibility of multi-axis machine, static flexibility of the entire machining system was taken into consideration. The multi-axis machining system was divided into the transmission axes-handle (AH) end and the cutting tool end. The equivalent shank method was developed to calculate the static flexibility of the AH end. In this method, static flexibility anisotropy of the AH end was considered, and the equivalent lengths of the AH end were obtained from calibration experiments. In cutter deflection modeling, force manipulability ellipsoid (FME) was applied to analyze the static flexibility of the AH end in arbitrary directions. Based on the synthetic static flexibility and average cutting force, cutter deflections were derived and estimated through developing program realization. The predicted results were compared with the experimental data obtained by machining 300 M steel curved surface workpiece, and a good agreement was shown, which indicated the effectiveness of the cutter deflection model. Additional experiments of machining flat workpiece were performed, and the relationship of cutter deflections and tool orientations were revealed directly. This work could be further employed to optimize tool orientations for suppressing the surface errors due to cutter deflections and achieving higher machining accuracy.

An Investigation of Workpiece Temperature in Orthogonal Turn-Milling Compound Machining

A thermal model estimating workpiece temperature in orthogonal turn-milling compound machining for the case with noneccentricity between rotation axes of workpiece and tool has been established in this paper. Milling tool and machining history were discretized into infinitesimal elements of equal size to deal with complicated cutter geometry and intermittent cutting procedure. The geometries of milling tool and workpiece were analyzed to calculate the instantaneous chip thickness, axial depth of cut, and angles of cutting entry and exit. Heat source during cutting process was considered as instantaneous moving rectangular heat source and heat conducting function in infinite solid thermal conductivity was developed. Experiments measuring cutting force and workpiece temperature were launched to test validity of this model and figure out the importance of effects those factors have on workpiece temperature from variance analysis of orthogonal experiment results. Furthermore, simulations to calculate peak temperature of workpiece were carried out by this model with relevant machining parameters and the results matched conclusions from experiment well.

An approach based on singular spectrum analysis and the Mahalanobis distance for tool breakage detection

The failure of cutting tools significantly decreases machining productivity and product quality; thus, tool condition monitoring is significant in modern manufacturing processes. A new method that is based on singular spectrum analysis and Mahalanobis distance are combined to extract the crucial characteristics from spindle motor current to monitor the tools condition. The singular spectrum analysis is a novel nonparametric technique for extracting the properties of nonlinear and nonstationary signals. However, because the components are not completely independent, the original singular spectrum analysis eventually leads to misinterpretation of the final results. The proposed method is used to overcome the weakness of the original singular spectrum analysis. The singular spectrum analysis algorithm is adopted to decompose the original signal and the useful singular values that correspond to the tool condition can be extracted. The Mahalanobis distance of the singular values is proposed as a feature that can effectively express the tool condition. The experiments on a CNC Vertical Machining Center demonstrate that this method is effective and can accurately detect the tool breakage in mill process.

NURBS curve interpolation algorithm adaptive to the machine's kinetic characteristics

NURBS curve interpolation algorithm for high speed NC machining, which can fit diverse machine tools kinetic characteristics and has the function of look-ahead control, is proposed. By integrating curve geometry features and machine tool dynamic characteristics, the look-ahead control information can be obtained. The interpolating process can be divided into two phases: getting the look-ahead control information including the particular points in the curve and their suitable max feed rate, modifying the real-time interpolation feed rate all the time according to the look-ahead control information. This algorithm has advantages over others on three aspects: wide adaptation to machine tool, high profile precision, and small feed rate vibration.

RCSA-Based Method for Tool Frequency Response Function Identification Under Operational Conditions Without Using Noncontact Sensor

The stability lobe diagrams predicted using the tool frequency response function (FRF) at the idle state usually have discrepancies compared with the actual stability cutting boundary. These discrepancies can be attributed to the effect of spindle rotating on the tool FRFs which are difficult to measure at the rotating state. This paper proposes a new tool FRF identification method without using noncontact sensor for the rotating state of the spindle. In this method, the FRFs with impact applied on smooth rotating tool and vibration response tested on spindle head are measured for two tools of different lengths clamped in spindle–holder assembly. Based on those FRFs, an inverse receptance coupling substructure analysis (RCSA) algorithm is developed to identify the FRFs of spindle–holder–partial tool assembly. A finite-element modeling (FEM) simulation is performed to verify the validity of inverse RCSA algorithm. The tool point FRFs at the spindle rotating state are obtained by coupling the FRFs of the spindle–holder–partial tool and the other partial tool. The effects of spindle rotational speed on tool point FRFs are investigated. The cutting experiment demonstrates that this method can accurately identify the tool point FRFs and predict cutting stability region under spindle rotating state. [DOI: 10.1115/1.4035418]