The localized faults of rolling bearings can be diagnosed by the extraction of the impulsive feature. However, the approximately periodic impulses may be submerged in strong interferences generated by other components and the background noise. To address this issue, this paper explores a new impulsive feature extraction method based on the sparse representation. According to the vibration model of an impulse generated by the bearing fault, a novel impulsive wavelet is constructed, which satisfies the admissibility condition. As a result, this family of model-based impulsive wavelets can form a Parseval frame. With the model-based impulsive wavelet basis and Fourier basis, a convex optimization problem is formulated to extract the repetitive impulses. Based on the splitting idea, an iterative thresholding shrinkage algorithm is proposed to solve this problem, and it has a fast convergence rate. Via the simulated signal and real vibration signals with bearing fault information, the performance of the proposed approach for repetitive impulsive feature extraction is validated and compared with the noted spectral kurtosis method, the optimized spectral kurtosis method based on simulated annealing, and the resonance-based signal decomposition method. The results demonstrate its advantage and superiority in weak repetitive transient feature extraction.

A New Family of Model-Based Impulsive Wavelets and Their Sparse Representation for Rolling Bearing Fault Diagnosis

Artificial intelligence systems for tool condition monitoring in machining: analysis and critical review

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American Society of Mechanical Engineers (ASME)

This paper presents a new S trajectory kinematic measurement method to evaluate the dynamic accuracy of five-axis machine tools based on R-test measurements. The S trajectory is obtained by scaling the machining path of the S-shaped test piece to the measuring stroke of the R-test. A geometric and dynamic accuracy simulation model is established to analyze the influence of various error factors on the S trajectory test and compare with the conical kinematic test described in ISO10791.6 quantitatively. The simulation results shown that the S trajectory test is more sensitive to most geometric errors and dynamic errors than the conical test. Particularly, to reflect the dynamic error factors such as poor rigidity of machine tools, servo mismatch, reverse error and nonlinear error, the S trajectory test has obvious advantages. Meanwhile, compared with the actual S-shaped piece machining, which is under development for inclusion in ISO 10791.7, the proposed non-cutting kinematic test method can simply reflect the dynamic accuracy of five axis machine tools itself without the interference of other factors and does not require additional workpiece and testing equipment. The proposed method is verified through experiments on a five-axis machine tool.

Dynamic accuracy evaluation for five-axis machine tools using S trajectory deviation based on R-test measurement

The modelling of volumetric errors of machine tools has been widely used by the method of Homogeneous Transformation Matrix (HTM) based on rigid body kinematics analysis for a long time. Without spindle induced errors and thermal errors, to establish a closed-loop HTM for a three-axis machine tool, the total of 21 geometric errors are the primary elements to be known. It is well known that the measured points of translational errors are directly related to the volumetric error at the tool cutting point through rigid body kinematics. In the generalized HTM method, however, this relationship is missing. This report, therefore, proposes a new comprehensive approach to formulate the volumetric errors based on the famous Abbe principle in order to derive the error term in the motion direction, and Bryan principle to derive the error terms in orthogonal to the motion direction. The proposed methodology is simple in concept, rational in physical meaning and easy in implementation. Experimental results, including faster multi-degree-of-freedom error measurements, volumetric error analysis and compensation on a testbed of small machine tool, validate the correctness and effectiveness of this method.

A novel modeling of volumetric errors of three-axis machine tools based on Abbe and Bryan principles

The invention discloses a two-dimensional code based quick parts selection method and system. The selection method includes the steps of measurement and computation, incorporation of information into two-dimensional codes, adhering of the two-dimensional codes, assembly of parts and the like. The selection system comprises a measurement and computation, an importing unit, an exporting unit and a selection unit, the measurement and computation unit measures and computes information of the parts, and the information of the parts is transmitted to the selection unit through the importing unit and the exporting unit for selection. The method and system has the advantages that by utilizing a two-dimensional code technology and combing a computation system, prescribed assembly accuracy and technical requirements can be guaranteed, to-be-assembled parts with appropriate tolerance are selected, and difficulty and cost of part machining are lowered.

Two-dimensional code based quick parts selection method and system

During five-axis CNC machining, the dynamic performance is the core factor to decide the efficiency and accuracy during high-speed and high-precision manufacturing. As a common method to detect dynamic performance of five-axis machine tools, measurement by using RTCP (Rotation Tool Centre Point) is always known as a better way than others with the advantages of high detection accuracy, variable detection trajectory and little interference. The key to effective detecting with RTCP function is the suitable trajectory, and in previous research, the 8-shape trajectory is proposed as an effective RTCP trajectory. In this paper, the 8-shape trajectory is adapted to machine tools with different rotary axes. The effects of the servo position gains, initial setup position, feed rate and on five-axis machine are shown in the simulation model, and the geometry and symmetry of the tool center point error trajectories are summarized to provide a guide to the improvement of dynamic performance.

RTCP Detection for Five-Axis CNC Machine Tool Dynamic Performance Based on 8-shape Trajectory

Nowadays the five-axis machine tool is one of the most important foundations of manufacturing industry. To guarantee the accuracy of the complex surface machining, multi-axis linkage performance detection and compensation of five-axis machine tools is necessary. RTCP (Rotation Tool Center Point) is one of the basic essential functions for the five-axis machine tools, which can keep the tool center with the machining trajectory when five axes move synchronously. On the basis of RTCP function, a way to detect multi-axes linkage performance of five-axis machine tools is briefly introduced, and linkage error model is built in accordance with the topological structure of machine tool. Based on the feature of the linkage errors of the five-axis machine tool, the error tracing and compensation method is proposed. Some simulations and experiments that verify the error tracing method could locate the linkage error category are established. Therefore, a new attempt to detect and compensate the linkage error of the five-axis machine tool is provided in this paper.

An Attempt of Error Tracing and Compensation Method of the Linkage Error of Five-Axis CNC Machine Tool

As an important nonlinear optical material, deuterated potassium dihydrogen phosphate (DKDP) crystal is used in laser beams as the core element of inertial confinement fusion. The most general method to produce smooth and crack-free DKDP surface is single point diamond fly-cutting (SPDF). However, the phase-changed temperature of DKDP is only about 120 °C which could be exceed in fly-cutting process. To analyze temperature field in cutting process, the formula based on the heat source method was introduced to calculate the temperature values on tool rake face under different cutting speed in DKDP crystal cutting process; then, thermo-mechanical FE analysis under the same process parameters was carried out to simulate the distribution of temperature field. The calculation and simulation results are basically in agreement, and the conclusion can be deduced: as the cutting speed increases, the temperature in the cutting zone increases, the highest temperature under common cutting parameter is up to 140 °C, which is validated by the dynamic infrared camera; however, the cutting temperature growth rate decreases with the same trend. The experiment results indicate that the chip morphology appears small spherical structure at high cutting speed, which illustrates the great possibility that the temperature exceed the phase transition temperature.

Study on thermal field in fly-cutting process of DKDP crystal

In the complex high speed machining, the small segments approximated the contours curve are made up the machining path in order to satisfy the quality. It will cause break on the machine tool feed-rate, and due to limit of dynamic performance in each axis, the actual velocity will somewhat differ from the desire feed-rate, which will cause additional error on the contour. An actual feed-rate prediction model using the G-code generating from CAM system is presented in this paper, which the limits of velocities, acceleration, jerk and the case of velocity verify between segments are taken into account, the every axis actual speed and tool feed-rate, and points that programming feed-rate is not achieved in the region of its curvature mutations are calculated. The simulation results show the prediction model is efficient and can support the analysis on axis dynamic performance in high-speed machining.

Wei Wang

Papers

Two-dimensional code based quick parts selection method and system

RTCP Detection for Five-Axis CNC Machine Tool Dynamic Performance Based on 8-shape Trajectory

An Attempt of Error Tracing and Compensation Method of the Linkage Error of Five-Axis CNC Machine Tool

Study on thermal field in fly-cutting process of DKDP crystal

Modeling of Feed-Rate Prediction for Small Segment in High Speed Machining