Chatter vibration has been a critical phenomenon in milling, and results in poor surface finishes, severe tool wear and shrill noise, which are usually overcome with quite conservative cutting parameters and hence the machining efficiency is significantly affected. In order to suppress the chatter vibration and improve the machining efficiency of milling process, a milling chatter mitigation method is presented with projection-based robust adaptive controller and an active magnetic bearing (AMB) installed in the milling spindle. The AMB is utilized to apply the active force to stabilize the milling process when the originally selected cutting conditions are unstable, with which the chatter-free boundary can be enlarged. Considering the possible parameters’ uncertainties of milling system which result from the nonlinear dynamic behaviors of the spindle system and the possible saturation of actuator caused by the noise, a projection-based robust adaptive controller is designed. Simulations of active chatter mitigation with different degrees of milling system’s uncertainties are performed, and the results show that the boundary of stability lobes diagram (SLD) of milling chatter is significantly enlarged. In addition, the milling experiments are also performed with the AMB installed in a milling spindle, and the results show that the chatter vibration is exactly mitigated with the presented method in this paper.

Rotary-laser automatic theodolite (R-LAT) system is a distributed large-scale metrology system, which provides parallel measurement in scalable measurement room without obvious precision loss. Each of R-LAT emits two nonparallel laser planes to scan the measurement space via evenly rotations, while the photoelectric sensors receive these laser plane signals and perform the coordinate calculation based on triangulation. The accurate geometric parameters of the two laser planes play a crucial role in maintaining the measurement precision of R-LAT system. In practice, the geometry of the two laser planes, which is termed as intrinsic parameters, is usually unknown after assembled. Therefore, how to figure out the accurate intrinsic parameter of each R-LAT is a fundamental question for the application of R-LAT system. This paper proposed an easily operated intrinsic parameter calibration method for R-LAT system by adopting coordinate measurement machine. The mathematical model of laser planes and the observing equation group of R-LAT are established. Then, the intrinsic calibration is formulated as a nonlinear least-square problem that minimizes the sum of deviations of target points and laser planes, and the ascertainment of its initial guess is introduced. At last, experience is performed to verify the effectiveness of this method, and simulations are carried out to investigate the influence of the target point configuration in the accuracy of intrinsic parameters.

The natural distribution of monitoring data is imbalanced, which has a negative impact on the training of intelligent diagnosis models. Although researchers have proposed data-level and algorithm-level methods to solve this problem, these methods are only applicable to small imbalance scenarios. In order to correct the anomalies of model training under large imbalance scenarios, this paper proposes a gradient harmonized loss that coordinates the gradients of each class to prevent the majority class in the imbalanced data from dominating the training. The coordination of gradients is based on the similarity of the sample gradients, and the compression of similar gradients is achieved by defining different penalty rules for each class. Taking into account the computational efficiency and the training difficulty, the proposed method is further optimized in terms of gradient dimensionality reduction and parameter simplification respectively. The proposed method was verified using two sample sets with different imbalance ratios and compared with traditional methods. The results showed that the proposed method greatly improved the performance of the DCNN model in large imbalance scenarios.

On-line detection and active control of chatter vibration have always been important issues in milling process respectively. To some extent, the signals obtained with sensors determine the performance of on-line detection and active control of chatter. However, due to the characteristics of milling process, the obtained signals are mainly consisted with spindle rotation frequency and its harmonics, and the chatter components are usually submerged by these stable harmonics, imposing negative effects for the detection and active control of milling chatter. Then, it is highly needed to design a real-time filter to filter out the spindle rotation frequency and its harmonics. In this paper, an adaptive filter is designed to filter out the spindle speed related components. Moving average (MR) model and adaptive filter theory is utilized to estimate these periodic components. The influence of filter order and step size factor on the filter characteristics are also analyzed. Considering that the filter order needs to be adjusted under different cutting conditions, which will alter the filter's performance, an improved adaptive filter is proposed. Experiments are also performed and the experimental results show that, not only the spindle speed related components can be filtered out effectively, but the chatter frequency components are amplified with appropriate initial step factor, which is beneficial for the detection of milling chatter at early stage. Meanwhile, the periodic components caused by the installation error and the other spindle speed related components can be effectively filtered out real-timely, preventing the saturation of actuator caused by these stable components.

A bionic hierarchy generative design algorithm inspired by the leaf vein growth process is presented for the layout design of heat conduction channels. The design domain is discretized based on the element-free Galerkin (EFG) method. The generations of main channels and lateral channels are separated. The effectiveness of the developed bionic hierarchy generative design approach is investigated based on the general “volume-to-point” heat conduction problem.

This paper proposes an explicit growth-based topology optimizer to generate optimal paths for a point robot moving in complex environments filled with obstacles. The idea is inspired by the intuitive analogy between a robot moving path and a heat transferring path. The feasible regions where a robot can pass through are defined as the design domain on which conduction heat transfer occurs, obstacles are modeled as thermal insulators, and the start and goal points are regarded as a heat source and heat sink. Based on this, the path planning problem is formulated as a topology optimization problem, in which the identification of heat transferring path is implemented by an adaptive growth procedure of high conductivity material link that minimizes thermal compliance. To make heat transferring paths (i.e., cooling channels) being able to grow freely within the design domain, a new method called the conductivity spreading approach (CSA) is developed to eliminate the growth dependency on the underlying ground structure. The suggested method is shown to be effective in all tested benchmark problems including path planning going through a stopover and problems involving more complex terrain conditions. This work suggests new potential applications of heat conduction topology optimization to non-traditional fields and is practically attractive to various path planning problems.

Self-excited vibration, widely referred to as chatter, has always been a limitation and challenge in machining. To suppress milling chatter vibration and improve surface finishes, a novel spindle system is proposed in this study. A noncontact electromagnetic actuator with two degrees of freedom is developed and integrated into the designed spindle system compactly. A differential driving mode is utilized for the electromagnetic actuator to obtain a linear output of actuator force, making the actuator more applicable for vibration control. Displacement sensors mounted near the actuator measure the vibration of the rotating spindle shaft and provide feedback signals for the developed proportional-derivative controller. The active damping performance of the designed spindle system with an integrated electromagnetic actuator, in both x and y directions, is also validated with impact tests and milling experiments, and a maximum increase (by factors of 3.67 and 2.89 in x and y directions, respectively) of dynamic stiffness at the first modal frequency is obtained. Milling experiment results with and without active damping also illustrate that milling chatter vibration has been well damped actively with the developed spindle system.

Rotate laser automatic theodolite system (R-LATs) is a distributed larger volume metrology system. With considering its excellent parallel measurement capability and the adaptive expansion of measureable space, R-LATs has a good prospect in large scale application, e.g. as a space measurement solution for an entire factory room to fix the spatial coordinate measurement, AGV navigation, and large component alignment etc. However, in large application scenario, where multiple theodolites are adopted, the photosensors suffer heavy working load in distinguishing the theodolite of each fan laser. It seriously restricts the real-time character, raises the probability of wrong signal generation, and degrades the work performance of R-LATs distinctly. To overcome this bottleneck, this paper proposed a lightweight framework for R-LATs to lighten the work load of photosensor in distinguishing the theodolites. Firstly, the working principle of R-LATs and the visibility of theodolite were introduced. Then, the whole frame work of R-LATs was designed in three aspects to relieve the work load of photosensor, i.e. topological network construction for entire R-LAT, data structure design for both compute terminal and photosensor, and the dynamic schedule of the data process unit for entire R-LATs. At last, by simulating AVG navigation in a large scale application of R-LATs, the effectiveness of this paper was proofed by comparing the computational loads with traditional configuration.

Milling chatter is a major factor limiting the machining efficiency and imposing poor surface finishes and machine tool damage, which is highly needed to be suppressed in the machining process. In order to control the unwanted chatter vibration, this research presents active milling chatter suppression using sliding mode control and electromagnetic actuator. The model of active milling chatter control system, with the electromagnetic actuator being considered, is presented firstly. In addition, the steady states caused by static milling force are neglected in the presented model. Then, an active sliding mode controller is designed, in which a dynamic output feedback sliding surface is introduced and the velocity state is not needed in the closed-loop system. The time delay item in the model are considered as disturbance, which makes the controller design easier. Simulation results show that the chatter-free domain is significantly improved in a wide spindle speed range. Milling experiments are also performed on a designed spindle system integrated with electromagnetic actuator, and the experimental results illustrate that the milling chatter can be well suppressed with the presented method and system, which shows advantages of robustness and practicality. (C) 2019 Elsevier Ltd. All rights reserved.

Many applications requiring dynamic tracking have been needed in large-scale. As a novel distributed measurement system, RLATs is presented and the key techniques are shown in detail. Because of the intrinsical drawback of distributed measurement systems, the Extend Kalman Filter approach is introduced to eliminate the tracking error and improve the tracking accuracy. State space model of RLATs are formulated, and an analytical expression for the linearized measurement function is derived. Comparison with the method of LS simulated data which presented a considerable improvement and stability in accuracy and the proposed EKF method while target’s moving speed is less than 100 mm/s.

The main error source effecting the mechanical precision of the machine spindle is the structural thermal deformation under temperature variation. So, we focused on temperature variation investigate of spindle in experiment approach. A magnetic loading device has been used for the measurement, which have a more compact stator and shorter axis length. Meanwhile, the FEM 3D analysis of the compact magnetic loader has been presented. By using this contactless loader, the temperature variation when spindles are rotating under different loads have been monitored and recorded. Experiment results show that the radial load has increased the temperature of spindle, but the higher speed directly weakened this influence. Furthermore, this experiment approach is verified and proved to be suitable for spindle tests.

When spindle rotates, the stiffness and natural frequency that reflect the dynamic performances of spindle system, vary with different rotating conditions. Therefore, the measurement of stiffness and natural frequency is highly needed. However, it is difficult to apply excitation to the rotating spindle during the measurement. In this paper, a non-contact electromagnetic loading device is developed to provide desirable excitation for the measurement. Next, an experimental spindle test rig with constant pressure preload is established. With the help of the proposed loading device, stiffness and natural frequency of the experimental spindle at different rotating states are measured. Finally, the effects of rotation speed and temperature on the natural frequency and stiffness of spindle are discussed based on the measurement results. The results show that the rotation speed and temperature have the similar influence trend on the experimental spindle’s softening.

In this paper, a novel radial loading topology is proposed for various spindle test application where the space in the tool head is limited or the performance to the length is sensitive. The stator of the loading device grows in the lateral direction, allowing for a compact axial length design. Finite element analysis (FEA) is carried out and the device design is optimized for the specifications of a radial loading device for high speed spindle. Finally, the designed device were manufactured and tested. By using this magnet loader, measurement results are given and the effectiveness of the designed prototype has been verified.

In the present work, the performance of oil-air two-phase flow under different lubricant oils was investigated. The simulation method was applied to study the influence of the oil viscosity on the flow pattern, velocity distribution and Re number in oil-air lubrication by FLUENT software with VOF model to acquire the working performance of oil-air lubrication for high-speed ball bearing. This method was used to obtain the optimum lubrication conditions of high-speed ball bearing. The optimum operating conditions that produce the optimum flow pattern were provided. The optimum annular flow was obtained by PAO6 oil with the low viscosity. Reynolds number influences the fluid shape and distribution of oil and air in pipe. The annular flow can be formed when Reynolds number is an appropriate value. The velocity distribution of oil-air two-phase flow at outlet was also discussed by different oil viscosities. The simulating results show that due to the effect of the oil viscosity and flow pattern the velocity decreased and expanded gradually close to the pipe wall, and the velocity increased close to the central pipe. The simulation results provide the proposal for the design and operation of oil-air two-phase flow lubrication experiments in the present work. This work provides a useful method in designing oil-air lubrication with the optimum flow pattern and the optimum operating conditions.

Active Magnetic Bearing (AMB) system has been used in higher rotating speed and higher precision rotor system, the influence of time-delay can't be neglected. The focus of this paper is presents the influence and demonstration of the system time delay effects on AMB system that has been usually disregarded. Then, we present both explicit formulas and numerical solutions to determine the maximum delay time which causes onset of system instability. Numerical simulation results of time delay effects on Single-DOF AMB system are presented in detail.