CNC Machine Tool Feed Research Articles

Research on Embedded Ball Screw Diagnosis System for Mechanical Fault Based on Bispectral Image

Ball screw is one of the main basic transmission components in CNC machine tool feed system because of its high transmission efficiency, positioning accuracy, and rigidity. It plays an irreplaceable role in the process of machine tool torque transmission and positioning. However, ball screw is also one of the parts which are easy to break down in the feed system. If it breaks down, it will affect the processing accuracy of the whole machine tool and even cause shutdown. Numerical control means that digital control is a high-efficiency technology that uses digital information to control mechanical movement and processing processes. Therefore, to increase the high-speed and high-precision operation ability of CNC machine tools, research and development of efficient and reliable predictive maintenance and issue identification technology to guide maintenance of CNC machine tools are critical. Throughout this study, a bispectrum image-based embedded defect fight against the disease for cylindrical gears is provided. Firstly, the bispectrum of fault signal is generated by Wavelet Packet Threshold denoising, wavelet packet reconstruction, and bispectrum analysis, and the characteristics of bispectrum are represented by the first kind of gray moments. These feature statistics are used as input feature vectors of BP neural network pattern recognition algorithm to classify these feature sets and identify the corresponding gear fault types. Experiments show that under the condition of noise, after 14.5 hours of testing, the NGI has increased significantly and can be used to diagnose faults in the gear system, and the method achieves relatively ideal recognition rate and verifies the feasibility of gear box fault diagnosis method based on image recognition. The code compiled by OpenCV library is easy to transplant to embedded system, with high development efficiency and reliable program operation. OpenCV has the characteristics of powerful matrix computing capability and convenient and flexible interface, and it is a general algorithm that can realize real-time image processing.

Ball Screw Fault Diagnosis Based on Wavelet Convolution Transfer Learning.

The ball screw is the core component of the CNC machine tool feed system, and its health plays an important role in the feed system and even in the entire CNC machine tool. This paper studies the fault diagnosis and health assessment of ball screws. Aiming at the problem that the ball screw signal is weak and susceptible to interference, using a wavelet convolution structure to improve the network can improve the mining ability of signal time domain and frequency domain features; aiming at the challenge of ball screw sensor installation position limitation, a transfer learning method is proposed, which adopts the domain adaptation method as jointly distributed adaptation (JDA), and realizes the transfer diagnosis across measurement positions by extracting the diagnosis knowledge of different positions of the ball screw. In this paper, the adaptive batch normalization algorithm (AdaBN) is introduced to enhance the proposed model so as to improve the accuracy of migration diagnosis. Experiments were carried out using a self-made lead screw fatigue test bench. Through experimental verification, the method proposed in this paper can extract effective fault diagnosis knowledge. By collecting data under different working conditions at the bearing seat of the ball screw, the fault diagnosis knowledge is extracted and used to identify and diagnose the position fault of the nut seat. In this paper, some background noise is added to the collected data to test the robustness of the proposed network model.

Mechanism-driven Method for Time-varying Error Modeling and Compensation of CNC Machine Tool's Feed Axes

Mechanism-driven Method for Time-varying Error Modeling and Compensation of CNC Machine Tool's Feed Axes

Application of a New Model Reference Adaptive Control Based on PID Control in CNC Machine Tools

To improve the control performance of the CNC machine tool feed servo system with nonlinear disturbances, a model reference adaptive control (MRAC) based on PID control is proposed. The method is based on the traditional three-loop control, the output signal of the speed loop controller is used as the input signal of the model reference adaptive controller, and the adaptive law is derived on the basis of Lyapunov stability theory. To verify the effectiveness, this paper analyzed the method through simulation and experiment. Results showed that the following error caused by nonlinear friction was significantly reduced when the speed was reversed, and the influence of noise and mechanical resonance was effectively suppressed. The proposed control method in this paper improves the motion-control accuracy and anti-interference ability of the control system.

Servo stiffness optimization of torque motor direct-drive CNC machine tool feed systems

Servo stiffness optimization of torque motor direct-drive CNC machine tool feed systems

MATLAB Simulation on Fuzzy PID Control to Feed Servo System of CNC Machine Tool

A CNC machine tool's feed servo mechanism is a dynamic electromechanical coupling system. It is difficult to correctly model the control mechanism due to the characteristics of time-varying parameters, load disturbances, and motor non-linearity. Intend to provide an approach where a fuzzy adaptive PID controller is designed by combining a PID controller with a fuzzy controller based on the mathematical model of the CNC machine tool fed servo system. Then intend to apply this controller to control the feed servo system to gain better control performance. The simulation results for the same are expected to show that this method not only has no static distortion, but also has a fast response with little overshoot, accounting for the high stability and accuracy of the fuzzy adaptive PID controller.

Study of dynamic vibration characteristics and suppression of CNC machine tool during operation

The rapid development of aerospace, automobile, national defense and other manufacturing industries has continuously improved the performance requirements of high speed and high positioning accuracy of the CNC machine tool feed system. As the thermal deformation error increases, the system structural rigidity decreases, the vibration increases, and accuracy of machine tool reduces. Existing research mainly focuses on the properties of mechanical and single thermal feed system, and less considers the dynamic performance under the action of thermal-mechanical coupling. For the improvement of feed system performance, it is very beneficiary. This paper takes the high-speed tool of CNC feed system as objective, combined with the actual working conditions to analyze the thermal characteristics, dynamic characteristics and vibration characteristics of the system under the effect of thermal-mechanical coupling. The thermal resistance and convective heat transfer of the key joint surface, the application of moving thermal loads, and the establishment of a simulation model to complete the steady-state temperature field, transient temperature field and thermal-structure coupling analysis. The results show that the maximum temperature rise of the feed system is 21.08 °C, The maximum thermal deformation is 17.264 um. The study found that the parameters such as flow rate and airflow temperature have a significant impact on the cooling effect, so the cooling device was further optimized. This paper proposes a control method for cutting chatter of CNC machine tools based on coupling of characteristics of thermal and mechanical. The thermal characteristic of the feed system and the thermal-mechanical coupling vibration characteristic test provides the maximum temperature error of 3.2 %, verifying the correctness of the theoretical method and analysis model. The highest temperature obtained by the test is 39.7 °C, indicating that the high-speed feed system has a large thermal effect. The relative error of the vibration amplitude of the test and simulation is 12.5 %, which verifies coupling in terms of thermal-mechanical. The accuracy of the vibration analysis method; the experiment depicts that the vibration amplitude increases by 19.7 % under the coupling effect of thermal and mechanical, indicating the effectiveness of dynamic characteristics of the high-speed feed system considering the thermal-mechanical coupling effect.

Dynamic model identification for CNC machine tool feed drives from in-process signals for virtual process planning

Virtual process planning offers advantages in terms of predicting servo and contouring errors ahead of time, and taking corrective action by modifying the program or CNC parameters. Successful application of virtual process planning requires accurate models that capture the dynamics of feed drives. Identification of such models is typically time consuming.This paper presents a pole search method used in conjunction with least squares (LS) projection technique for identifying virtual machine tool drives. Compared to earlier research published in rapid identification, and the generic system identification method (i.e., a two-stage instrumental variable method), the parameter convergence has been improved significantly. This is achieved by reducing the number of unknown variables solved during LS estimation from eight to four (corresponding to each candidate pole triplet), and by avoiding the use of noisy position measurements and their time derivatives in the LS matrix pseudo-inversion. As a result, virtual feed drive models can be constructed using only in-process gathered data, without interrupting a machine tool's production for dedicated identification tests. Effectiveness of the new method is demonstrated in simulations and experimental case studies on two different machine tools, a gear grinding machine, and a 5-axis machining center. With the new method, servo errors can be predicted during the process planning stage to within 1-2% of closeness of their actual (experimental) values.

Analysis on Dynamic Contact Characteristics and Dynamic Stiffness Estimating Method of Single Nut Ball Screw Pair Based on the Whole Rolling Elements Model

The purpose of this paper is investigating the characteristics of dynamic contact and dynamic stiffness of the single nut ball screw pair (SNBSP). Then a new sensorless method is proposed to extract the SNBSP dynamic contact stiffness of a mass production CNC machine tool feed system. First of all, the transformation relationship between each coordinate system of SNBSP is established. Secondly, the dynamic model of all ball–raceway contact pairs is established. Based on this, a dynamic contact stiffness model is established. The dynamic contact parameters are obtained by the numerical method. It is found that the influence of screw speed on screw and nut raceway normal force distribution are opposite. This will affect the variations of dynamic contact stiffness. It is also clear that the effect of axial load on dynamic stiffness is significant. Then, an effective method is proposed to estimate the dynamic contact stiffness of a mass production CNC machine tool feed system without any external sensors. The axial force of feed system is estimated by using torque current of servo motor. Current signals can be obtained through FANUC Open CNC API Specifications (FOCAS) library functions, and then dynamic contact stiffness can be calculated through the stiffness model without external sensors. Finally, a feed system dynamic model is built, and the contact model and sensorless stiffness estimating method are verified by experiments in this dynamic system.

Thermal–Mechanical Coupling Analysis and Experimental Study on CNC Machine Tool Feed Mechanism

As the CNC machine tool feed mechanism is affected by joint action of heat and load during the working process, thermal–mechanical coupling analysis and experimental research on CNC machine tool feed mechanism are conducted. On the basis of exploring the thermal–mechanical coupling effect of CNC machine tool feed mechanism, a thermal–mechanical coupling dynamic analysis method is proposed through combining multi-step finite element simulation with temperature field experiment. According to the proposed method, the transient and steady-state simulation analysis on CNC machine tool feed mechanism are conducted and conclusions obtained are as follows, before the whole feed mechanism reaches thermal balance state, the thermal–mechanical coupling effect makes the deformation of the feed mechanism increase with the temperature rising. The correctness of the proposed thermal–mechanical coupling dynamic analysis method was verified by the contrastive analysis of the experiments. Therefore, in the process of CNC machine tool feed mechanism’s analysis and design, the influence of thermal–mechanical coupling effect on dynamic performance should be considered.

Iterative NC program modification and energy saving for a CNC machine tool feed drive system with linear motors

This study proposes a design of iterative learning contouring controller (ILCC) by considering actual contour error compensation (ACEC) to enhance the contouring performance of CNC machine tool feed drive systems with linear motors. The ACEC with linear and circular interpolation is designed to estimates contour error precisely. The proposed control iteratively modifies the numerical control (NC) programs for each drive axis to reduce a contour error. Hence, the proposed approach can be directly applied for a commercial CNC machine tool with linear motors currently in use without any modification of their original controllers. Both of linear and circular interpolations are verified by simulation in both air-cutting and machining condition. The simulation is conducted for a non-smooth rhombus and circular trajectory. The effectiveness of the proposed methods has been experimentally verified through a CNC machine tool with linear motors for a non-smooth rhombus trajectory. Experimental results show that the proposed controller could reduce the maximum and mean contour errors by 94.58% and 88.67% on average, respectively. The proposed method improved the control input variance by 37.9%, and consequently energy consumption was reduced by 11.7% compared with the original NC program.

Optimal Design of Electromagnetic Force of Hidden—Pole Magnetic Suspension Linear Motor

In order to eliminate the frictional resistance of CNC machine feed platform and improve the machining accuracy and surface roughness, the hidden - pole magnetic suspension linear synchronous motor used to drive the CNC machine tool feed platform was studied. According to the special structure and operation mechanism of the hidden - pole magnetic suspension linear motor, the mathematical model of the electromagnetic force of the motor was established firstly. Then the finite element calculation for the air gap magnetic density, back electromotive force and electromagnetic force of two different structures of the motor of the salient pole and hidden pole was carried out by Finite element software, and the harmonic analysis for air gap magnetic density was done. By comparing the electromagnetic forces of the two motors, it is found that the hidden pole has less fluctuation of the electromagnetic force, so it is more suitable for feed platform as a driving component. Finally, Particle swarm optimization is used to optimize the electromagnetic force of the hidden-pole controlled-magnet linear magnetic suspension synchronous motor, which further reduces the fluctuation of the electromagnetic force, and also improves the efficiency of the motor. The results of the experimental prove the effectiveness of the control method.

A novel dynamic contour error estimation and control in high-speed CNC

High-speed CNC machining requires high-precision servo response and dynamic performance of feed drives with better control parameters matched in coupled axis. In this paper, an electromechanical coupling system of multi-axis CNC machine tool feed drive model is established for servo parameter optimization and high-precision contour error improvement. The influences of the joint stiffness and the friction disturbance in servo dynamic have been considered. The disturbance parameter and joint stiffness have been identified by unbiased least squares scheme. The electromechanical coupling model is used to study the contour error estimation and compensation technology in high-speed machining. The multi-axis contour error is estimated by using Ferguson curve to approximate the curve between the interpolation points. The calculation is fast and accurate enough for contour error pre-compensation. Experiments prove that five-axis contour error can be effectively reduced by dynamics pre-compensation in high-speed CNC with better processing quality and stability improvement.

Comparison of accuracy stability using a thermal compensator and grating ruler

The disadvantages of the closed-loop control of CNC machine tool feed drive systems using grating rulers were analyzed, including the reason why thermal compensators cannot be widely used on machine tools. A new modeling method based on the heat transfer theory for half-closed-loop feed drive systems is proposed to solve the poor robustness of commonly used thermal models, and the modeling and parameter optimization procedures are presented. In the new modeling method, the thermal errors caused by ambient temperature variation and ball-screw friction were calculated separately. Based on the heat production, heat conduction, and heat convection theory, the ball-screw temperature field at any given time can be obtained to predict the ball-screw thermal errors. Experiments were conducted on a vertical machining center VMC1100p, and the test process, compensation principle, and communication configuration between the compensator and CNC are presented. Finally, the accuracy stability of a half-closed-loop feed drive system after the compensation was found to be far higher than that before the compensation, and also far higher than that obtained under closed-loop control using a grating ruler.

Thermal Error Modeling Method for a CNC Machine Tool Feed Drive System

The disadvantages of the common current thermal error modeling methods for CNC machine tool feed drive systems were analyzed, such as the requirement of many temperature sensors to reach high accuracy and poor applicability of different moving states. A new robust modeling method based on the heat transfer theory is proposed, and the procedure of the thermal tests for a feed drive system is presented. Multiple regression method and robust modeling method based on the heat transfer theory were, respectively, used to establish a thermal error model, and a pointer automatic optimizer was used to optimize the parameters in the robust model. A compensation simulation was conducted under five different moving states using these two modeling methods, and the advantages of the robust modeling method were proved. Finally, the compensation effect of the robust modeling method was verified under a random moving state on a vertical machining center.

Fuzzy PID Control To Feed Servo System of CNC Machine Tool

The feed servo system of CNC machine tool is a complex electromechanical coupling system. Due to the characteristics of time-varying parameters, load disturbances and motor nonlinear, it is difficult to model for the control system accurately. An approach is presented that a fuzzy adaptive PID controller is designed by the PID controller combined with the fuzzy controller based on the mathematical model of the CNC machine tool feed servo system. The controller is applied to control the feed servo system and gained better control performance. The simulation results show that this method not only has no static distortion, but also has a fast response with little overshoot. This fuzzy adaptive PID controller has high stability and accuracy.

Modelling and simulation of a feed drive using the transmission line modelling technique

The paper focuses on the modelling and simulation of a test rig and a digital drive is based on the transmission line modelling technique. The rig is a positioning system equivalent to a CNC machine tool feed drive. Accurate representations of dynamic systems included in electromagnetic, power electronic and some mechanical applications have been obtained until now by applying the transmission line modelling technique. The paper proposes a novel application of th~s method for simulation of closed loop control of the position of a test rig. The model includes the distributed parameter dynamics of the feed drive and the effect of mass distribution. This is based on the flexibility of transmission line modelling to develop lumped and distributed parameter systems. Also a transmission line model for the controller integrated into the digital drive is developed. Encouraging simulation results are obtained by using MATLAB. In this way, the CNC machine tools feed drives could be modelled with increasing accuracy as hybrid, distributed-lumped representations using numerical methods.

CAD for CNC machine tool main spindle and feed drives

Characteristics of main spindle and feed drives for the CNC machine tool highly depend upon skillfulness of composing variable speed motors (AC or DC) and mechanical transmission elements. In order to enable interactive computer aided design and analysis of different design variants of CNC machine tool drives, original computer programs have been developed.