Real Machine Tool Research Articles

FROM THE TRADITIONAL MULTILATERATION TO THE INTEGRATED MULTILATERATION APPROACH: A ROADMAP TOWARDS THE AUTOMATIZATION OF VOLUMETRIC ERROR MAPPING PROCESS FOR LARGE MACHINE TOOLS

Multilateration-based volumetric error mapping is gaining widespread adoption in the coordinate measurement machine and machine tool industry as the most effective approach for geometric characterization of large-size machines. In the traditional method, tracking interferometers are placed on the machine table while the measurement retro-reflector moves with the spindle. However, this approach has several limitations, including manual instrument manipulation and a sequential measurement scheme that hinders unattended execution. To overcome these limitations, the integrated multilateration method has been introduced, which addresses these challenges and reduces measurement uncertainty. This method offers the potential for fully autonomous volumetric error mapping of large-size machines and enables the development of new functionalities such as traceable coordinate measurement with large machine tools. This research presents the roadmap followed by the authors to automate the volumetric error mapping process for large machine tools. It outlines the current status of the technology, starting from the conceptual development and culminating in the experimental results obtained from real industrial machine tools.

게임엔진 기반 갠트리형 공작기계의 디지털 트윈 구현

With the advent of the Fourth Industrial Revolution, digitalization has been accelerated, and interest in digital twins has grown in tandem with technological advancements. In this study, we developed a realistic and interactive digital twin system using a game engine. We focused on a dual-servo gantry-type machine tool and employed the Unreal Engine to create a virtual environment, while using Arduino as a gateway for data communication. Our system facilitates the transfer of virtual machine tools using real machine tool data and allows for the emergency stop of real machine tools through virtual machine tool emergency stop signals. By ensuring real-time data communication and bi-directionality between the real and virtual systems, we successfully produced a highly realistic simulation system.

An extended LuGre model for estimating nonlinear frictions in feed drive systems of machine tools

Nonlinear frictions in feed drive axes affect the control accuracy and dynamic of the machine tools. Conventional dynamic friction models neglect the position-dependent friction, caused by manufacturing errors and misalignment as well as the environment. This paper proposes an extended LuGre friction model for estimating the dynamic and position-dependent friction effects. The conventional LuGre model is modified by a position-dependent term, which describes the nonlinear friction behavior of machine axes with long travel distance. An online data-driven identification approach is developed to fast parametrize and update the model. The suggested method is validated on a real machine tool.

Experiencing the structure and features of a machine tool with mixed reality

Augmented and mixed reality (AR/MR) enable a completely new way of visualizing the connections between components and assemblies of a complex machine tool. By means of AR/MR, users can immerse themselves in areas of interest of a machine or an assembly process and not only observe the connections from outside a real machine or a process. Experiencing virtual contents in the real surroundings is completely different from virtually seeing a design or an assembly process on a screen by means of a conventional CAD application or a simulation. Therefore, this paper presents a mixed reality app for the visualization of information about components and assemblies in the holograms of a complex machine tool.Within a research project on the improvement of teaching methods by augmented reality (AR), virtual reality (VR) and mixed reality (MR), it is planned to concept, develop and test teaching units in studies. At the Institute for Machine Tools (IfW) of the University of Stuttgart, the Index R200 high-end turning/milling centre has been chosen as demonstration model for an MR app. It is a 10-axis machining centre with several driven spindles and tool holders in the working space. It can be used both as real machine tool for complex experiments and as virtual machine for simulations or visualizations of CNC programs, among other things for developing new teaching methods and contents.

Predicting the position-dependent dynamics of machine tools using progressive network

The structural dynamics of a machine tool exhibit position-dependent behavior under operation due to the kinematic reconfiguration of its feed drives. Experimental identification of position-dependent dynamics can be time-consuming, and simulation models may lack accuracy due to modeling uncertainties. In this paper, the prediction of a machine tool's position-dependency is approached under the progressive network, a transfer learning technique to bridge the gap between the simulation and real-world domains. The dynamics simulation model may be somewhat inaccurate, but still describes a machine tool's overall position-dependency. The real-world domain is then characterized by sparse dynamics measurements made on the real machine tool. Under the progressive network architecture, a neural network is first trained in the simulation domain to extract valuable prior knowledge about the machine's position-dependency. A second network posed in the real-world domain then accesses such prior knowledge from the simulation domain via lateral connections to improve its dynamics predictions. Such transfer learning methodology may be most advantageous when the number of experimental data is limited, and the machine is unavailable for further testing due to production purposes. The proposed methodology was validated under numerical and experimental studies.

Ukryte naruszenia bezpieczeństwa w układach automatycznego sterowania procesami technologicznymi

The progressing automation and robotization in the industrial plants as well as the increasing complexity of the control systems of integrated machines make it necessary to constantly improve the functional safety of machines through the correct validation of safety systems. Despite the validation process carried out, the potential software errors may reveal during the usage of the machine as hidden security breaches. The article presents examples of security breaches of real machine tools and attempts to implement solutions of automated mechanisms for detecting security problems. Another aspect of the article is the new approach for detecting hidden security breaches. Using the „digital twin” model of the machine, a program that generates a sequence of events for testing control systems, and the use of a virtual reality (visual verification of the safety programs), it is possible to maximize the functional safety functions of the machine.

Drive axis controller optimization of production machines based on dynamic models

The paper deals with the creation and implementation of a methodology for optimizing the parameters of cascade control of the machine tool axis drives. The first part presents the identification of a dynamic model of the axis based on experimental data from measuring the axis dynamics. The second part describes the controller model, selection of optimization objective functions, and optimization of constraint conditions. The optimization of controllers is tuned by simulation using identified state-space model. Subsequently, the optimization procedure is implemented on the identified model, and the found control parameters are used on a real machine tool linear axis with different loads. The implementation of the proposed complex procedure on a real horizontal machine tool proved the advantage of simultaneous tuning of all parameters using optimization methods. The strategy solves the problem of mutual interaction of all control law parameters disabling effective usability of gradual sequential tuning. The methodology was developed on a speed control loop, the tuning of which is usually the most difficult due to the close interaction with the dynamic properties of the machine mechanics. The whole procedure is also applicable to the position and current control loop.

Chatter Stability Prediction and Process Parameters’ Optimization of Milling Considering Uncertain Tool Information

Stability is the prerequisite of a milling operation, and it seriously depends on machining parameters and machine tool dynamics. Considering that the tool information, including the tool clamping length, feeding direction, and spatial position, has significant effects on machine tool dynamics, this paper presents an efficient method to predict the tool information dependent-milling stability. A generalized regression neural network (GRNN) is established to predict the limiting axial cutting depth, where the machining parameters and tool information are taken as input variables. Moreover, an optimization model is proposed based on the machining parameters and tool information to maximize the material removal rate (MRR), where the GRNN model is taken as the stability constraint. A particle swarm optimization (PSO) algorithm is introduced to solve the optimization model and provide an optimal configuration of the machining parameters and tool information. A case study has been developed to train a GRNN model and establish an optimization model of a real machine tool. Then, effects of the tool information on milling stability were discussed, and an origin-symmetric phenomenon was observed as the feeding direction varied. The accuracy of the solved optimal process parameters corresponding to the maximum MRR was validated through a milling test.

Virtual reality training platform for a computer numerically controlled grinding machine tool

In-depth training of machine tool (MT) operators is crucial to avoid machine damage due to faulty operation. However, machine-hours are costly and during the training, the MT is unavailable for regular production purposes. Here, virtual real-size models offer a solution by providing basic operation principles to future operators. In this context, it is yet unknown whether a virtual teaching enhanced by real walking is similar to a real teaching scenario regarding the learning efficiency and long-term memory retention. This paper describes a study comparing the learning efficiency of a virtual training session with traditional instructions on a real MT. The learning success of both training groups is objectively and subjectively assessed on a real MT a week later. In this assessment, the task completion time and the number of errors are recorded. We observed that the virtually taught group slightly outperformed trainees taught in reality regarding both objective measurements.

Validation of a hardware-in-the-loop simulator for investigating and actively damping regenerative chatter in orthogonal cutting

Machine tool productivity and part surface quality are fundamentally limited by chatter occurring due to regenerative type self-excited vibrations. Efficacy of the existing high-fidelity chatter models to help avoid chatter in real industrial settings remains limited due to the uncertainties in machine tools. To help validate models without the vagaries of the uncertainties and without damaging real machine tool systems, this paper discusses the use of a mechatronic hardware-in-the-loop (HiL) simulator that offers a platform for investigation on chatter. The HiL simulator is a hybrid system of hardware and software components substituting the actual cutting tool-workpiece interaction through an actuator exciting a flexure by an emulated real time cutting force. For the simulator to faithfully represent the physics of the process-machine interactions, experimentally characterized stability behavior with the HiL must necessarily follow model predictions. However, the transfer between the hardware and the software layers of the HiL simulator involves inevitable delays that result in diverging stability behavior. We hence present systematic investigations to identify and compensate the delay in the hardware layer on account of the actuator and the transducers, as well as delays in the software layer on account of signal conditioning. The validated HiL simulator is then used as an experimental platform to investigate the effectiveness of four different control strategies for an active damping system. Being a non-destructive, cost-effective and repeatable platform, the HiL simulator opens up further possibilities for validation of high-fidelity chatter models.

Validation of machining operations by a Virtual Numerical Controller Kernel based simulation

A Digital Production Twin of a machine tool can be accomplished with the Common Simulation Engine (CSE) based on a Virtual Numerical Controller Kernel (VNCK) of a corresponding control of a machine tool. The main advantage of the VNCK simulation lies in the detection of syntax errors, which cannot be found via a 3D-simulation. As a result, the Numerical Control (NC) code can be regarded as validated except the used machining data. In this paper, a method is presented which can validate the complete NC code before it is tested on the real machine tool.

Investigating the learning performances between sequence‐ and context‐based teaching designs for virtual reality (VR)‐based machine tool operation training

AbstractBackgroundTraining workers in machine tool operations is indispensable. Because training course at school with real machine tools is costly and dangerous, most researchers have concentrated on developing and adopting virtual reality (VR)‐based applications. However, to improve students’ learning performance levels, teaching design is imperative.PurposeThis study hopes to investigate the performance differences between sequence‐ (traditional) and context‐based teaching designs along with a self‐developed VR computer numerical control (VRCNC) training environment.MethodExperimental design, sequence‐ and context‐based teaching designs were developed for this study. Forty male senior students were recruited from the department of mechanical engineering at an industrial high school. Then, corresponding pretests, teaching activities and posttests were implemented based on the proposed teaching and experimental designs. Finally, experiment‐, questionnaire‐, and interview‐based performance evaluations were utilized to conduct the final comparison and conclusion.ResultsAveragely, the context‐based teaching design exhibited superior results for mostly the learning performances. The survey results also revealed that the students obtain more satisfaction and self‐confidence after the context‐based teaching.ConclusionsAccording to the results, the context‐based teaching design has obvious improvement on the performance of machine tool operation training. Three types of evaluation results provides a comprehensive support for the proposed context‐based teaching design along with the VRCNC in machine tool education.

An energy-efficient process planning system using machine-monitoring data: A data analytics approach

This paper presents a system development of incorporating Computer-Aided Process Planning (CAPP) with energy-efficient machining based on a hybrid approach to take advantage of Generative Process Planning (GPP) and Variant Process Planning (VPP) and compensate for the drawbacks of both GPP and VPP. The GPP decides process plans without human assistance through decision-making algorithms in computers but lacks in ensuring the models’ robustness for different machining conditions. The VPP adopts group technology by reusing existing plans through the identification and classification of part family but does not support predictive and optimum decision-making. The developed Energy-Efficient Process Planning System (EEPPS) builds upon data analytics to efficiently process the machine-monitoring data collected from real machine tool’s operations and to develop energy prediction and optimization models based on historical machine-monitoring data. Particularly, those energy prediction and optimization models allow process planners to anticipate the energy consumed during executing a numerical control program and optimize process parameters at the level of machining features for minimizing energy use. This paper also presents a prototype implementation to show the feasibility of the proposed EEPPS.

Development of Real Time Machine Tools Component Utilization Data Acquisition for developing Dynamic Model of Maintenance Scheduling

Maintenance scheduling accuracy of CNC machine tools components should be calculated based on actual data utilization of each component. Actual usage of each component can be approached by component grouping based on machine operation phase utilization, which is divided into Power-On, cutting and noncutting phase. This paper describes a study on development of machine monitoring data utilization for obtaining real time information of spindle and machine axis positions as well as current consumption of spindle servo motor. Data collection was conducted by a termination method on wiring feedback control of spindle encoder signal and axes encoder signals. On the other hand, current consumption of spindle servo motor was measured by a CT current transducer. Afterward, a WEMOS microcontroller was used to process and to transfer data wirelessly to a Raspberry which acted as a broker. The data will used to update the data status of CNC Machine Tools utilization database, where it was communicated by using a MQTT protocol. A monitoring system has been developed and resulted the real time information of machine phase utilization. It will be further utilized as primary data input for building a dynamic maintenance model.

Five-axis machine tools accuracy condition monitoring based on volumetric errors and vector similarity measures

Abstract The accuracy of a machine tool affects the geometry and dimensions of machined parts. A machine tool accuracy condition monitoring scheme using volumetric errors (VEs), vector similarity measures (VSMs) and exponentially weighted moving average (EWMA) control chart is proposed in this research. The usefulness of this scheme is tested with simulated machine error data as well as real machine tool tests using NC induced geometric error changes and a real C-axis encoder fault. Both sudden and gradual changes were considered for the simulated faults. The results show that VE is a meaningful quantity for the monitoring of the machine tool accuracy condition. The proposed VSMs work well in VEs feature extraction. Amongst the studied VSMs, the module of the vectorial difference of two consecutive VE vectors (Dist) and the angle between those vectors (Cos2) are more stable and perform better for monitoring faults with sudden and gradual changes than the remaining VSMs in real VE data processing. Finally, this research provides guidelines for the use of VEs as well as a VE-based monitoring strategy for monitoring machine tool accuracy condition.

A new approach to geometric error modeling and compensation for a three-axis machine tool

This paper proposes a new geometric error model and compensation algorithm for the three-axis machine tools. First, the relative motion matrix to the coordinate system is constructed by the homogenous transformation matrix (HTM). Next, the geometric error model is deduced based on homogenous transformations. Then, an error compensation algorithm is developed by means of the computer numerical control (CNC) program reconstruction by using the geometric error model. Finally, the simulation is implemented on a virtual machine tool established in the VERICUT software to validate the efficiency of the model and the compensation algorithm. An autocollimator is used to measure the yaw errors and an experiment is implemented on a real machine tool. The results simulation and experiment indicate that the error modele and compensation algorithm can significantly improve the machining precision.

New approach for bearing life cycle control

This paper presents a new approach for the control of the life cycle of bearings in machine tools. A new simulation tool has been developed using the well-known ISO 281 standard as a reference. This new tool improves the accuracy of the estimations in two fields: model-based and feature based prognostics. On the one hand, the tool is able to provide accurate end-of-life estimations thanks to the determination of accurate component loads for a defined manufacturing cycle. In addition, this new tool is able to be embedded in monitoring devices in order to use real machine tool usage data and calculate Remaining Useful Life of the analysed component. This last application can be combined with vibration monitoring of the bearing in order to detect unexpected component degradation.

Research on the EDM Technology for Micro-holes at Complex Spatial Locations

For the demands on machining micro-holes at complex spatial location, several key technical problems are conquered such as micro-Electron Discharge Machining (micro-EDM) power supply system’s development, the host structure’s design and machining process technical. Through developing low-voltage power supply circuit, high-voltage circuit, micro and precision machining circuit and clearance detection system, the narrow pulse and high frequency six-axis EDM machining power supply system is developed to meet the demands on micro-hole discharging machining. With the method of combining the CAD structure design, CAE simulation analysis, modal test, ODS (Operational Deflection Shapes) test and theoretical analysis, the host construction and key axes of the machine tool are optimized to meet the position demands of the micro-holes. Through developing the special deionized water filtration system to make sure that the machining process is stable enough. To verify the machining equipment and processing technical developed in this paper through developing the micro-hole’s processing flow and test on the real machine tool. As shown in the final test results: the efficient micro-EDM machining pulse power supply system, machine tool host system, deionized filtration system and processing method developed in this paper meet the demands on machining micro-holes at complex spatial locations.

Study on Construction Method of Geometry Simulation Environment of Eight-axis with Five-axis Linkage Machining Center

In order to solve the machining geometry simulation of an eight-axis with five-axis linkage boring and milling machining center produced by JOBS company in Italy, in this paper, the structure of geometry simulation environment was designed based on the analysis of functional requirements, the geometric constraint relations and motion relations of machine tool was analysed, the machine model, control model and measurement analysis model was built, and the machining geometry simulation environment was established that had the same all functions, characteristics and behaviours with real machine tool. The practical application shows that the simulation environment can factually reflect the static and dynamic characteristics of machine tool; the measurement analysis function can effectively ensure the quality of processing products and the safety of machine tool. The construction method of geometry simulation environment can provide a technology and method reference for constructing numerical control machining geometry simulation environment of other types multi-axis machine tool.

Effect of Honing Parameters on Generated Surface Quality of Cylinder Liner within Automotive Engine Production

One of the key parameter in evaluation of cylindrical surface quality of the engine liners is surface roughness. A large number of process factors affecting a final surface topography, which has direct impact on fuel consumption and CO2 emission. A suitable choice of honing conditions can results not only to better surface quality, but it can contributes to reducing of environmental impacts in automobile transport. Twelve different engine cylinder liners were machined in various combinations of cutting parameters. Experimental testing was realised on real production machine tool, where process factors were cutting speed, machining allowance and stone pressure of honing tool. All factors have 4 levels and parameters of surface roughness CR, CF, CL were selected as a variables and suitable indicators for surface quality assessment. The results show that influence of the tool stone pressure on honed surface is more significant than effect of cutting speed. Effect of machining allowance is negligible as well.