Multi-axis Computer Numerical Control Research Articles

Fixation of pelvic acetabular fractures using 3D-printed fracture plates: a cadaver study

Open reduction and internal fixation of pelvic acetabular fractures are challenging due to the limited surgical exposure from surrounding abdominal tissue. There have been a number of recent trials using metallic 3D-printed pelvic fracture plates to simplify and improve various elements of these fracture fixation surgeries; however, the amount of time and accuracy involved in the design and implantation of customised plates have not been well characterised. This study recorded the amount of time related to the design, manufacture and implantation of six customised fracture plates for five cadaveric pelvic specimens with acetabular fracture, while manufacturing, and surgical accuracy was calculated from computed tomography imaging. Five of the fracture plates were designed within 9.5 h, while the plate for a pelvis with a pre-existing fracture plate took considerably longer (20.2 h). Manufacturing comprised 3D-printing the plates in Ti6Al4V with a sintered laser melting (SLM) 3D-printer and post-processing (heat treatment, smoothing, tapping threads). The manufacturing times varied from 27.0 to 32.5 h, with longer times related to machining a thread for locking-head screws with a multi-axis computer numerical control (CNC) mill. For the surface of the plate in contact with the bone, the root-mean-square errors of the print varied from 0.10 to 0.49 mm. The upper range of these errors was likely the result of plate designs that were relatively long with thin cross-sections, a combination that gives rise to high thermal stresses when using a SLM 3D-printer. A number of approaches were explored to control the trajectories of locking or non-locking head screws including guides, printed threads or hand-taps; however, the plate with CNC-machined threads was clearly the most accurate with screw angulation errors of 2.77° (range 1.05–6.34°). The implanted position of the plates was determined visually; however, the limited surgical exposure and lack of intra-operative fluoroscopy in the laboratory led to high inaccuracies (translational errors of 1.74–13.00 mm). Plate mal-positioning would lead to increased risk of surgical injury due to misplaced screws; hence, it is recommended that technologies that can control plate positioning such as fluoroscopy or alignment guides need to be implemented into customised plate design and implantation workflow. Due to the plate misalignment and the severe nature of some acetabular fractures comprising numerous small bone fragments, the acetabular reduction exceeded the clinical limit of 2 mm for three pelvises. Although our results indicate that customised plates are unsuitable for acetabular fractures comprising six or more fragments, confirmation of this finding with a greater number of specimens is recommended. The times, accuracy and suggested improvements in the current study may be used to guide future workflows aimed at producing customised pelvic fracture plates for greater numbers of patients.

Energy-aware sub-regional milling method for free-form surface based on clustering features

Geometric characteristics and curvature of free-form surfaces have a great influence on multi-axis computer numerical control (CNC) machining performances such as processing efficiency, surface quality and energy consumption. The conventional machining methods with the whole tool path generation results in poor low machining efficiency, surface quality, and high energy consumption, due to the repeated and crossing tool path. Therefore, this paper proposes an energy-aware milling method for complex surface based on clustering features. Firstly, the geometric features of free-form surfaces are classified according to their curvature characteristics. Then, free-form surface is discretized and initially divided into different regions, and further divided into patches based on K-means clustering algorithm to generate the same or similar surface type. Moreover, an optimization model for the sub-regional milling tool path is established, and the optimal result is obtained using adaptive dynamic genetic algorithm. Finally, the effectiveness of the proposed method is verified by comparison of traditional milling methods.

Rapid construction method of equipment model for discrete manufacturing digital twin workshop system

A large-scale manufacturing workshop includes a wide variety and a large amount of equipment. When equipment is mapped as a digital twin (DT) model, the DT model has complex and implicit or non-hierarchical relationships, which makes the development of a DT workshop system (DTWS) for a manufacturing plant challenging. To address this problem, this paper proposes a rapid construction method of equipment model (RCMEM) for a discrete manufacturing DT workshop system, which can meet the requirements of complex manufacturing business scenarios, improve the efficiency and quality of the DT model construction at the equipment level, and form an efficient equipment model construction method. First, a DT object (DTO), which represents a basic unit of the DT model, is defined. The DTO is used to derive the DT model at the equipment level. The DTO collects and wraps generalization-capable functions from equipment into components, and geometric, functional, and communicative descriptions are combined into a single model. The DT model can increase the scalability, reusability, and modeling quality by reusing the DTO capabilities. Further, a general construction process of the DTO model of multi-axis computer numerical control (CNC) machines is presented. This process standardizes the common capabilities of the equipment models and minimizes the construction time of machines’ DT models. Furthermore, a rapid mounting and communication configuration mechanism (RMCCM) is proposed. This mechanism enables fast DTO network communication and improves interoperability in a multi-source data environment. This paper also proposes a DTWorks Software development kit, which can help developers to build digital factory standalone applications. The RCMEM is implemented into the DTWorks. Finally, a real DTWS case is used to examine the differences in equipment model building before and after the application of the RCMEM. The results demonstrate the good effectiveness of the RCMEM in complex business settings.

Development of low-cost heterodyne interferometer with virtual electronic phasemeter

Commercial laser interferometers are conventionally used to measure the positioning error of a long linear stage in multiaxis computer numerical control machine tools. However, commercial laser interferometers are costly and difficult to use. Therefore, a low-cost photodetector-based heterodyne interferometer combined with an electronic phasemeter module was proposed for precise measurement of the positioning error of a long linear stage. The proposed heterodyne interferometer was combined with a virtual electronic phasemeter that employs a self-developed signal-processing technique. Our core algorithm and proposed photoelectric-signal-processing technique were developed using the LabVIEW human–machine interface. Moreover, to verify the performance of the proposed heterodyne interferometer, a laboratory-built prototype was constructed and used to measure the positioning error of a long linear stage. The experimental results indicated that the positioning accuracy of the proposed interferometer was ±4.5 μm for a linear stage with a displacement of 250 mm; the results obtained were comparable to those obtained with a commercially available laser interferometer. The proposed heterodyne interferometer can thus be used in other applications related to precision engineering.

Influence of Ball-End Milling Strategy on the Accuracy and Roughness of Free Form Surfaces

Freeform surfaces are present on an increasing number of engineering products. Three- and multi-axis computer numerical control milling machines are commonly used for improved production. Computer-aided manufacturing (CAM) systems are used almost exclusively for the creation of programs for a variety of machining centers. This study compared the quality of freeform surfaces made by 3- and 5-axis milling using three commonly used strategies (linear, offset, and spiral). The CAM system-predicted surfaces were also compared with the actual surfaces. A test sample with a freeform surface was used for the experiments. Considering the size and distribution, the discrepancy between the predicted surface deviations and the deviations in the produced samples was proven. Maximum negative surface deviations, when 5-axis milling, employed linear and spiral strategy of 29% and 71% less than those produced by the 3-axis milling. On the contrary, positive deviations were 48% smaller. A comparison of the scans showed that the two strategies (linear and spiral) yielded better results for 5-axis milling, and the offset strategy was better for 3-axis milling. Evaluation of the achieved surface roughness showed that the milling method did not significantly affect the surface quality in the linear strategy. However, other two strategies (offset and spiral) achieved better results with 5-axis milling compared to 3-axis milling. The proposed method of evaluating the accuracy of machined free form surfaces can be used in experimental as well as production activities.

Investigation of isotropic radiation of low energy X-ray intra-operative radiotherapy by MAGAT gel dosimeter

PurposeIsotropy as a quality assurance aspect of intraoperative radiotherapy (IORT) needs to be evaluated accurately. There are some main problems associated with isotropy investigations by two dimensional dosimeters including limited positions and distances in which isotropy can be measured and long irradiation time needed for isotropy evaluation. In this study, isotropic radiation accuracy of spherical applicators of low energy X-ray IORT was estimated by the use of MAGAT gel as a three dimensional gel dosimeter and a specified IORT phantom. MethodsDesigned IORT phantom was manufactured by multi-axis computer numerical control machine (CNC) using Plexiglas. To investigate isotropy, methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel dosimeters embedded in the phantom holes were irradiated with a 50 kV X-ray IORT device to 18 Gy at the surface of the vials. Then, relative dose deviations of output doses from their average were extracted from MRI images of the gel vials in different positions and distances from the 50-mm spherical applicator. ResultsThe percentages of relative deviations of output doses from the average value were less than 8% in all positions which are within the 15% acceptance limit of isotropy radiation. Moreover, a Pearson-moment correlation analysis showed a Pearson's r equal to 0.99–1 for different polar and azimuth angles representing isotropic radiation emission of X-ray IORT. ConclusionIsotropy of IORT can be easily investigated using gel dosimeters by applying the produced phantom which solved the issues facing three-dimensional measurement of isotropic radiation of IORT X-ray source (XRS).

Digital twin control of multi-axis wood CNC machining center based on LinuxCNC

This paper presents an application of an open architecture control system implemented on a multi-axis wood computer numerical control milling machining center, as a digital twin control. The development of the digital twin control system was motivated by research and educational requirements, especially in the field of configuring a new control system by “virtual commissioning”, enabling the validation of the developed controls, program verification, and analysis of the machining process and monitoring. The considered wood computer numerical control (CNC) machining system is supported by an equivalent virtual machine in a computer-aided design and computer-aided manufacturing (CAD/CAM) environment, as well as in the control system, as a digital twin. The configured virtual machines are used for the verification of the machining program and programming system via machining simulation, which is extremely important in multi-axis machining. Several test wood workpieces were machined to validate the effectiveness of the developed control system based on LinuxCNC.

A New Analytical Path-Reshaping Model and Solution Algorithm for Contour Error Pre-Compensation in Multi-Axis Computer Numerical Control Machining

Abstract Reduction of contour error is crucial for multi-axis computer numerical control (CNC) machining to produce products with required geometric and dimensional accuracy. Although various contour error pre-compensation methods have been developed, few studies are dedicated to five-axis machines when compared with three-axis ones. In this paper, a new contour error pre-compensation method that integrates analytical prediction of contour error, optimal path-reshaping model, and decoupling solution algorithm is proposed for five-axis machining. First, by analyzing the dynamic responses of servo drive to the typical step and ramp signals, linear expression of servo tracking error with respect to the sequence of discrete axis positions is yielded for the prediction of contour error ahead of servo loops. Then, using the Taylor-series expansion and the pseudo-inverse matrix of the Jacobian function, a least-square optimization-based path-reshaping model that implies the satisfaction condition of zero contour error is analytically built. Thus, the complicated nonlinear contour error pre-compensation problem is converted into a simple quadratic programming problem. Concerning the effects of tool orientation reshaping on tool-tip contouring accuracy, a simple yet effective synchronous compensation strategy is subsequently proposed, through which both tool tip and tool orientation contour errors are reduced to near-zero without any iteration. To address the neighbor-dependence of the contour error compensation in adjacent cutter locations, a progressive solution algorithm with linear computational complexity is also briefly presented. Both numerical simulations and laboratorial experiments are conducted to validate the effectiveness of the proposed method.

On-line contour error estimation and control for corner smoothed five-axis tool paths

The dimension accuracy of the part is directly affected by the contour error. The improvement of contour accuracy has been one of the research hotspots in five-axis Computer Numerical Control (CNC) machining. Because of the inexplicit mathematical expressions of the point-to-curve distance function for free-form parameterized splines, most existing contour error estimation algorithms of the multi-axis CNC machining are based on linear or circular approximation, while the geometric characteristics of the tool path are not taken into account. However, the corner smoothed five-axis tool paths are composed of straight lines and micro splines with few control points, which have clear and simple mathematical expressions and make it possible to directly calculate the contour error from the actual tool pose to the reference tool path. Considering the geometric characteristics of the corner smoothed five-axis tool paths, this paper proposes an on-line and high-accuracy contour error estimation algorithm for five-axis CNC machining. The estimated contour error components of each axis are compensated to the position-loop controller of each axis to realize contour error control. Simulation and experimental results show that the proposed method has higher precision than the state of art methods, and contour errors are effectively suppressed by on-line compensation.

Estimation of scallop height in freeform surface CNC Machining

Scallop height is primarily used to assess the quality of complex freeform surface parts manufactured on multi-axis computer numerical control (CNC) machines. Currently, the inspection methods used in practice are slow and expensive as they need sophisticated equipment and skilled personnel. No simulation technique seems to exist to estimate the part quality a priori. This paper reports the development of a software system to estimate the scallop heights for freeform surface machining from the CNC part programs. Two approaches have been proposed. The first one processes the CAD model of the machined component obtained from the simulation software while the second approach directly processes the CNC toolpath to generate scallop points on the surface. The scallop points generated from both approaches are analyzed to estimate scallop heights at various regions on the surface using numerical curve fitting techniques. The developed system was extensively tested for different surface types, toolpath strategies and the results from the machining trials. The system was found to be robust and accurate to estimate the part quality a priori.

Kinematic modeling and machining precision analysis of multi-axis CNC machine tools based on screw theory

This paper presents the solution to evaluate and predict machining precision of a multi-axis computer numerical control (CNC) machine tool. The “function-motion-action” method is used to describe the motion relationships of a multi-axis CNC machine tool, and the multi-body system structure model of the machining system is further constructed. By analyzing the motion process of the machine tool based on the meta-action layer and considering the motion transfer relations in meta-action chains, the kinematic models of each motion shaft are established in twist exponential form. According to the structural and kinematic relationships of these motion shafts, the kinematic and kinematic error models of the machine tool can be easily obtained. Then, the distance error formula is used to deduce the general model of machining allowance error. A simulation test and practical experiment are performed on a type of CNC controlled 5-axis machining center. The experiment results show that the proposed method is universal, and it can greatly simplify the kinematic analysis of multi-axis CNC machine tools.

Comparison of Manufacturing Data Analysis For 5 & 3-Axis Vertical Machining Center for the Time and Tool Benefits of Industries

The dawn of globalization of business and competitiveness in manufacturing has forced firms to enhance their manufacturing facilities to reply to plug necessities. One of the crucial factors for this is often machine evaluation that involves a crucial decision using general and obscure information. The Primarily mass production aims high productivity so as to reduce cost and interchangeability to facilitate simple assembly which necessitates the production devices to increase the speed of manufacture. Across the business, the assembly challenges pivot around cutting lead times, increasing throughout and obtaining products to market as quickly as possible alongside some less challenging problems like shorter runs, higher product combine, tighter tolerances, a lot of complicated geometries in harder materials, and complete machining during a single handling. Advancements in technology have resulted in a creation of a lot of responsive tools referred to as MTM systems that are computer numerical Control (CNC) systems capable of acting a variety of operations with multiple tools and spindles in a single setup. The following project aims at reduction of manufacturing cost by modifying the process layout and operational parameters by novel approach for an identical element for 3 and 5- Axis Vertical Machining center. Nowadays, machining layout and operational sequence plays a significant role in automotive business to produce products at competitive price in market which consists of Machines, Tools, fixtures, computer interface, trained professionals and form of products. MAKINO PS60 is a Multi axis CNC machine (BRIDGE PORT), that helps to perform the machining operations on the roles at 5 totally different axes to create the required profiles whose implementation can pave means for a few terribly important benefits like, seven machines are replaced by Single machine, Man power are reduced from 9 to 3 per day, Tools usage reduced from 40 to 30 per day & production cost can reduce up to 60%.

An Analytical C3 Continuous Local Corner Smoothing Algorithm for Four-Axis Computer Numerical Control Machine Tools

Linear motion commands of multi-axis computer numerical control (CNC) machine tools need to be smoothed at the transition corners, because the velocity discontinuities at corners can result in fluctuations on machine tool motions and lead to poor surface quality. However, no research has been reported on local corner smoothing algorithm for four-axis CNC machine tools with two rotary axes by considering their special kinematic characteristics. To this end, this paper proposes an analytical C3 continuous local corner smoothing algorithm for four-axis CNC machines with two rotary axes. After coordinates transformation, the tool tip positions and tool orientations are smoothed by locally inserting specially designed three-dimensional (3D) quintic B-splines and one-dimensional (1D) quintic B-splines into the corners between linear motion segments, respectively. The smoothing algorithm guarantees C3 continuity of the tool tip position and C3 continuous synchronization of the tool orientation related to the tool tip position, through analytically evaluating control points of the inserted microsplines. The maximum error tolerances of the tool tip position and tool orientation are mathematically constrained. Experiments on an in-house developed four-axis machine verify the efficacy of the proposed algorithm, where maximal errors caused by the local corner smoothing algorithm are constrained, the synchronization of the tool orientation and the tool tip position are achieved, and the proposed C3 continuous corner smoothing algorithm has lower jerk and jounce but higher tracking and contour accuracy than C2 continuous algorithm.

Development of a modular computer-aided process planning (CAPP) system for additive-subtractive hybrid manufacturing of pockets, holes, and flat surfaces

Additive manufacturing (AM) can significantly reduce the development time for small batch parts or parts with complicated geometries. However, the accuracy of most metal AM processes requires parts to be subjected to secondary processing (typically machining) in order to obtain requisite tolerances. Process plan development for hybrid manufacturing, which is defined for the following as additive manufacturing followed by subtractive multi-axis computer numerical control (CNC) machining, typically takes weeks rather than hours or days. This paper outlines a feature-based advanced hybrid manufacturing process planning system (FAH-PS) that uses feature-specific geometric, tolerance, and material data inputs to generate four-automated process plans based on user-specified feature precedence for hybrid manufacturing. FAH-PS currently has the capability to identify manufacturing processes for critical pockets, flat surfaces, and hole features. Additional plans generated by FAH-PS minimize tool changes, orientation changes, etc., to improve process times. FAH-PS is modular and extensible to allow for additional feature types, materials, tool sizes, and/or optimization strategies to be included in future versions. A case study, using a custom patient-specific bone plate, demonstrated system capabilities and processing time reductions as compared to the current manual process planning for hybrid manufacturing methodologies. Using the generated FAH-PS process plan resulted in a 35% reduction in machining time from the current hybrid manufacturing strategy. Imploring a strategy of minimizing tool and orientation changes generated a process plan that demonstrated that even further improvements were possible.

A Graphics Processor Unit-Accelerated Freeform Surface Offsetting Method for High-Resolution Subtractive Three-Dimensional Printing (Machining)

Machining is one of the major manufacturing methods having very wide applications in industries. Unlike layer-by-layer additive three-dimensional (3D) printing technology, the lack of an easy and intuitive programmability in conventional toolpath planning approach in machining leads to significantly higher manufacturing cost for direct computer numerical control (CNC)-based prototyping (i.e., subtractive 3D printing). In standard computer-aided manufacturing (CAM) packages, general use of B-rep (boundary representation) and non-uniform rational basis spline (NURBS)-based representations of the computer-aided design (CAD) interfaces make core computations of tool trajectories generation process, such as surface offsetting, difficult. In this work, the problem of efficient generation of freeform surface offsets is addressed with a novel volumetric (voxel) representation. It presents an image filter-based offsetting algorithm, which leverages the parallel computing engines on modern graphics processor unit (GPU). The compact voxel data representation and the proposed computational acceleration on GPU together are capable to process voxel offsetting at four-fold higher resolution in interactive CAM application. Additionally, in order to further accelerate the offset computation, the problem of offsetting with a large distance is decomposed into successive offsetting using smaller distances. The performance trade-offs between accuracy and computation time of the offset algorithms are thoroughly analyzed. The developed GPU implementation of the offsetting algorithm is found to be robust in computation, and demonstrates a 50-fold speedup on single graphics card (NVIDIA GTX780Ti) relative to prior best-performing algorithms developed for multicores central processing units (CPU). The proposed offsetting approach has been validated for a variety of complex parts produced on different multi-axis CNC machine tools including turning, milling, and compound turning-milling.

A method for grinding face gear of double crowned tooth geometry on a multi-axis CNC machine

The stability requirement of bearing contact and a favorable function of transmission errors motivates the investigation of design and manufacture technology of the face-gear drives. Application of a grinding disc wheel with axial profile modification and a longitudinal ease-off topography design of face gear tooth flanks could be proper utilized to obtain a double crowned tooth geometry, which results in the pre-designed bearing contact and desired transmission errors. With the profile crowned tooth geometry of the gear generated by the modified wheel cutter, finding of the execution motions to generate the tooth geometry with the longitudinal ease-off topography design on a multi-axis Computer Numerical Control (CNC) machine with the same tool is a major issue. Therefore, a universal method on the Design Optimization Techniques is proposed to obtain the execution motions for such problem. The proposed optimization methodology is also applicable for the tooth flank error correction by a worm hob or a grinding cutter on the CNC generator. With the term of additional movement of execution motion is defined, a detailed description of additional movements for the ease-offs of the real crowned tooth geometry is also investigated. The feasibility of proposed method is validated by numerical examples.

A review of contouring-error reduction method in multi-axis CNC machining

Abstract With the rapid development of aerospace, energy, and power technologies, the demand for high-performance parts with complex curved surface is increasingly large, and the multi-axis Computer-Numerical-Control (CNC) precision machining technique for such parts becomes a popular and difficult issue in the industrial field. In order to ensure the high-performance of complex curved surface parts, the requirement of the contour accuracy is higher and higher for such parts due to the important role they play in these fields. However, the limitation of dynamic properties for the CNC machine tools, which leads to the contouring-error, becomes a vital issue that affects the machining accuracy of the high-performance parts with complex curved surface. The contouring-error, defined as the orthotropic distance from the actual motion position of machine tool to the desired contour of curved surface in multi-axis contour-following tasks, is caused by the facts such as servo lag, dynamics mismatch, external disturbances, and so forth. The reduction of the contouring-error becomes of great significance for promoting the performance of CNC motion systems thus realizing the high-speed and high-precision machining, and the research on the contouring-error reduction in multi-axis CNC machining is therefore a hotspot issue in the machining engineering. This paper provides a comprehensive review to the state of the art of the contouring-error reduction methods. The massive and complicated studies on constraining the contouring-errors are classified and summarized, and accordingly, the advantages and the disadvantages of different kinds of methods are discussed and compared, which has a guiding significance for selection of the interested contouring-error reduction method. Furthermore, this paper systematically suggests the probable future studies that remain vacant and meaningful based on the discussion of the state of the art. Significantly, it is possible for active promoting and developing to further improve the contouring-error reduction of the complex curved surface parts in multi-axis CNC machining.

Intelligent Computer-aided Process Planning of Multi-axis CNC Tapping Machine

The increasing complexity of the manufacturing industry demands computer numerical control (CNC) machining, a massively used process that is equipped with an intelligent feature. Not only does its control function revitalize competition in a sustainable manufacturing ecosystem but also advances the Industry 4.0 readiness. This paper develops an intelligent computer-aided process planning (i-CAPP) based on two widely accepted performance measures: manufacturability and efficiency. Machine tapping is a very popular CNC machining process making threaded holes, from which there is an investigation of two manufacturability scenarios. The first scenario deals with all holes with the same size that undergo the same operation (OP). The second one handles the groups of holes with different sizes machined by various OPs. Meanwhile, the study of efficiency focuses on point-to-point drilling, tapping, and chamfering. This research work verifies such indicators by proposing hybrid-two-stage optimization algorithms: 1) traveling salesman problem and 2) innovative Tabu Search. The i-CAPP verification of both indicators was confirmed in an application with a five-axis CNC tapping machine to realize the Industry 4.0 readiness. Extensions of the research in the pursuit of higher intelligent manufacturing platforms are discussed.

Development and application of software for open and soft multi-axis EDM CNC systems

This study aimed to develop software for multi-axis electrical discharge machining (EDM) computer numerical control (CNC) systems using open CNC technology and soft CNC technology and to then apply the software to the machining of rimmed turbine blisks. Through the analysis of functional requirements, this study established the hierarchy structure of the software. On the basis of this structure, three main modules and their communications were established with Linux and RT-Linux as the development platforms. The software architecture was also constructed. Through the construction of the modules and communications and the realization of the functions, the multi-axis EDM CNC system software was developed and installed into a five-axis EDM CNC machine to realize the machining of rimmed turbine blisks. Machining results show that the architecture of the software is correct, harmonious, and reasonable. The software is also stable and reliable and features strong real-time capability and accurate movement control.

Modeling and identification of the multi-axis drive system using support vector machine and granular computing

Advanced manufacturing technology requires high-precision capability in multi-axis computer numerical control (CNC) machine tools. At present, the modeling and identification for the drive system of CNC machine tools has some defects. In order to solve the problem, some interdisciplinary theories and methods, such as support vector machines, granular computing, artificial immune algorithms, and particle swarm optimization algorithms, have been used to model and identify multi-axis drive systems for CNC machine tools. An identification method using a support vector machine, based on granular computing, is presented to identify a multi-axis servo drive system model for improving the precision of model identification, and an immune particle swarm optimization algorithm, based on crossover and mutation functions, is proposed to optimize the structure parameters of the support vector machine based on granular computing. The proposed identification method was evaluated by experiments using the multi-axis servo drive system. The experimental results showed that the proposed approach is capable of improving modeling and identification precision.