CNC Controller Research Articles

Adjustability improvement of face-milling spiral bevel gears by modified radial motion (MRM) method

In recent years, the development of CNC hypoid generator has made it possible to perform nonlinear correction motions for the cutting of the face-milling spiral bevel and hypoid gears. The existing lengthwise curvature modifications are primarily achieved by changing the cutter diameter or the cutter blade pressure angle with tilt cutter axis. However, both lengthwise curvature modifications need to rebuild the head cutter. In this paper, a methodology is proposed to improve the adjustability of the spiral bevel gear assembly by modifying the radial motion of the head cutter in the machine plane of the hypoid generator. The head cutter is unchanged in the proposed method. Therefore, the adjustability for gear assembly can be on-line controlled by a CNC controller without dismounting and rebuilding the head cutter. The numerical results show that the bearing contact ratio is virtually the same as initial design while the adjustability is increased dramatically.

Neural-Network-Based Numerical Control for Milling Machine

We describe a device which uses a neural network to generate part-programs for milling, drilling and similar operations on machining centres, on the basis of 2D, 2.5D or 3D geometric models of prismatic parts, without operator intervention. The neural network consists of networks for prediction of milling strategy, for prediction of surface quality and for the optimisation of technological parameters in milling. We introduce the surface complexity index (SCI) for identifying surfaces which are very difficult to machine. The SCI takes the surface roughness and machining strategy into account. Teaching and testing of the NN is described. The device, which can be retrofitted to a CNC controller, can be trained from a set of typical parts and will then generate new NC part-programs. A case study of a tool used in the automotive supplier industry shows how a milling strategy is proposed, according to set constraints.

An innovative software architecture to improve information flow from CAM to CNC

Abstract Over the years, machine tool evolution has allowed faster equipment, using new configurations, to manufacture parts that were almost impossible to machine in the past. Despite this tremendous evolution in machine and control technologies, the metalworking industry is still using the old ISO 6983 G-Codes programming interface to control the motion of these machines. This programming interface is not the most flexible or most appropriate for use by new open-architecture machine controllers and object-oriented high-level machining interfaces such as ISO 14649 (STEP-NC). This work proposes an innovative language, the ‘Base Numerical Control Language (BNCL),’ which is based on a low-level simple instruction set-like approach. The architecture is designed around two concepts: the BNCL virtual machine, which acts as a virtual microprocessor, and the BNCL virtual hardware, which is an abstraction of the machine tool. The language is characterised by its simplicity and flexibility, two qualities that are critical in a market in which the capabilities and performance of machines are constantly improving. The proposed architectural concepts are validated through various computer simulation and physical tests, including performance throughput, trajectory driving, and CNC controller extension capabilities.

On STEP-NC and the Complexities of Product Data Integration

For twenty years the manufacturing domain has been seeking to share product model data by defining an entity relationship model covering the life cycle of geometrically defined products. The data sharing is implemented by selecting subsets of these entities and relationships to define data exchange standards for CAD, CAE, CAM, CNC and PDM systems. The approach requires agreement on how data will be reused across the domains so an organization has been meeting to manage the required data definitions. Considerable success was achieved in 1995 when a standard was proposed and implemented by industry as a way to move 3D geometry between CAD systems. Now, a new protocol for exchanging manufacturing process information between CAM systems and CNC devices is being released. This protocol reuses much of the data defined for the other domains and will allow CNC manufacturing tools to process 3D data, but the complexity of the specification is causing controversy. In this paper we report on the new specification and analyze the advantages and disadvantages of its approach to defining CNC control programs.

ISO6983NCデータから次世代CNCデータISO14649への変換(S60-2 生産システムの新展開(2),S60 生産システムの新展開)

The technical information, such as Machining feature, type of machining operation and machining condition, is necessary for operator to use NC code in the shop floor. However, NC code has no relation each other in explicit form. Then, it is difficult to manage, modify, and verify NC data. Therefore this is the cause of the human error. In this research, the technical information is extracted from NC code, and the technical information is transformed into a next-generation CNC control language(ISO 14649) which contains the technical information. In this report, Workingstep is constructed from Machining feature, Machining strategy and Approach-Retract strategy which are extracted from NC code based on Form-shaping function.

434 ISO14649ベース加工システムとISO6983NCデータの変換(OS5 生産システムとCAD・CAM)

The technical information, such as Machining feature, type of machining operation and machining condition, should be integrated in one data structure with some relation between these information in order to manage, modify, and verify NC data and avoid the human error. In this research, the technical information is extracted from NC code, and the technical information is transformed into a next-generation CNC control language (ISO 14649) which contains the technical information, and the ISO 14649 data is stored in XML database. In this report, Workingstep is constructed from Machining feature, Machining strategy which are extracted from NC code based on Form-shaping function. ISO 14649 Machining system is also developed.

Study on a reconfigurable model of an open CNC kernel

Based on a behavioral model, in this paper a new dynamic modeling method is presented and used to analyze the life cycle of application objects and their interactions in an open-architecture CNC controller model. Since a CNC kernel has a high capability real-time multi-task controller, it is important to develop CNC software based on non-real-time preempt multi-task operating system (Windows NT). A proper method for software high capability real-time control is employed when open on CNC kernel is designed. Further, the paper develops a solution for how to realize reconfigurable structures in CNC systems and seamless connection between function modules and a system.

Architecture and implementation of a shop-floor programming system for STEP-compliant CNC

STEP-NC (formalized as ISO 14649 and ISO 10303 AP238) is a new interface (or language) standard for the CAD–CAM–CNC chain, currently under establishment by ISO TC184 SC1 and SC4. Upon completion, it will replace ISO 6983, so called M & G codes used for CNC since 1950s. As the new language is being established, a new CNC controller called STEP-CNC (STEP-compliant CNC), capable of carrying out various intelligent tasks using the new language as an input, receives worldwide attention. Shop-floor programming (SFP) system is a computer-assisted part programming system interfaced with STEP-CNC. Its primary function is to generate part program in ISO 14649 (or STEP AP238) to machine the part geometry given by STEP AP203 or AP224 file. In this paper, we first present an architecture for the SFP system, followed by implementation technology including: (1) STEP physical file interpretation, (2) feature recognition, (3) process planning, (4) part program generation, and (5) verification. The developed methodology was implemented in a prototype called PosSFP, and tested with Korea STEP-NC system.

Error measurement of five-axis CNC machines with 3D probe–ball

This paper presents a new measurement device and corresponding method for an accuracy test of five-axis CNC machines. This device is named probe–ball, and consists of a 3D probe, an extension bar and a base plate with a measuring ball on one side. The 3D probe has a standard taper and is capable of three-degrees-of-freedom displacement measurement. The extension bar has a socket at its free end. A permanent magnet is integrated in the socket so that the extension bar and the measuring ball can be connected together with magnetic force. After installing the probe–ball device, the kinematic chain of the five-axis machine tool is closed. To measure the accuracy of five-axis machine tools, curves on a spherical test surface are defined as tool paths. The tool orientation is defined in the surface normal direction. The center of the spherical test surface coincides with the center of the measuring ball. With this path and orientation input to CNC controller, the 3D probe moves relative to the measuring ball on the spherical test surface. The overall positioning errors of the relative motion are measured by the 3D probe and are used to justify the volumetric accuracy of the five-axis machine.

Robustification of CNC Controllers for Machine Tools Motor Drives

This paper presents a methodology for enhancing the robustness of a CNC controlled system by convex optimisation of the Youla parameter. The methodology requires as a first step the design of an initial polynomial controller. This controller is then robustifled considering temporal and frequency constraints, which are formulated by means of the Youla parameterisation within a convex optimisation framework. The optimal Youla parameter is finally obtained by solving this optimisation problem. In this way, a compromise between robustness and closed loop behaviour can be easily managed. An application to the position control of an induction motor drive is presented, where the robustness of different controllers (PID or GPC) regarding model uncertainties in high frequency is enhanced while respecting a temporal template for the disturbance rejection.

112 Development of a Sub-pixel Optical Vision System for Precision Tool Setting

Precise and efficient tool setting technique and accurate tool shape monitoring are of essential importance in ultra-precision diamond turning operation. The traditional way of tool setting are typically laborious, inefficient and rely heavily on experience. A big part of the tool setting is done by using a contact probe such as LVDT. The contact tool setting station can normally, depending on the resolution of the probes, place the tool tip to within a 1∿10μm positioning accuracy. However, it is running the risk of damage the delicate tool tip and has the ambiguity introduced by contact point of tool and touch probe. The optical/non-contact way of setting the tool do have the advantage of not having to touch the tool, but its resolution is limited by the optical diffraction limit and the resolution of the CCD device used (mm/pixel). A non-contact precision tool setting system is developed and built in this study using edge-detection image processing and sub-pixel dividing techniques in conjunction with CNC controller of the precision turning machine to improve the system presently available. The results showed that tools of different shapes namely round, half-round and sharp tool could all be positioned to within an error band of ±0.1μm by using the developed tool setting system.

Thermal Error Measurement and Real Time Compensation System for the CNC Machine Tools Incorporating the Spindle Thermal Error and the Feed Axis Thermal Error

Thermally induced errors have been significant factors affecting machine tool accuracy. In this paper, the thermal spindle error and thermal feed axis error have been considered, and a measurement/compensation system for thermal error is introduced. Several modelling techniques for thermal errors are also implemented for the thermal error prediction; i.e. multiple linear regression, neural network, and the system identification methods, etc. The performances of the thermal error modelling techniques are evaluated and compared, showing that the system identification method is the optimum model having the least deviation. The thermal error model for the feed axis is composed of geometric terms and thermal terms. The volumetric errors are calculated, combining the spindle thermal error and feed axis thermal error. In order to compensate for the thermal error in real-time, the coordinates of the CNC controller are modified in the PMC program. After real-time compensation, the machine tool accuracy improved about 4-5 times.

Compensation of systematic errors in five-axis high-speed machining

A method is described for the compensation of errors associated with tool path generation, particularly during five-axis high-speed machining (HSM). Information on machine tool performance and its dynamic features is used to calculate possible errors and convenient modifications of the NC program, thereby avoiding errors when parts are actually being machined. This 'preprocess method' by means of postprocessing with NC software is presented. The errors dealt with are mainly servo lag errors, but the explored approach can support most systematic errors associated with machine tool performance. These are briefly summarized. Research so far has largely been aimed at the implementation of compensation routines in the CNC controller and at corrections in real time. The problem is that most applications are only available for three-axis milling. The presented approach (compensation before machining by using software routines in a specially designed postprocessor) is based on a fuzzy logic expert system. The benefits can be summarized as data reduction, data improvement, precontrol of feed, and improved component accuracy. The applied procedure is also convenient for implementation in an industrial environment by retrofitting existing equipment. The suggested method provides improved control over machine dynamics, permitting high-speed machining centres to maintain a maximum or near-maximum feed rate despite axis reversals and tool path changes, even at corners. Two categories of results are presented, namely the management of NC data related to expected performance of the machine tool and improvements of the machine tool performance in terms of productivity and accuracy of the machined test components.

Product Development Methodology for Machine Tools

In machine tools industry, new product developments with global competitiveness are urgently required. In particular, a man-machine interface for machine tools plays a dominant role in success or failure in new product developments. Nevertheless, a desirable man-machine interface for CNC controller has not been investigated in the previous academic literatures. Performances of man-machine interface largely influence on usefulness or acceptability of the machine tools. In this study, therefore, a usability measure with multiple attributes was defined based on the results of interview investigations with some mature operators. And also, a structured method for identifying the important design items was proposed. Using the proposed method, mutual relationships among the design items of control panel of CNC controller were identified to improve usability.

Developing an integrated STEP-compliant CNC prototype

Abstract STEP-compliant CNC is the next-generation CNC controller, taking the STEP-NC data model as the interface scheme between CAM and CNC and carrying out various intelligent functions. At the moment, efforts are being made worldwide to establish an international standard for the new interface scheme (so-called STEP-NC), formalized as ISO 14649. In the near future, the new interface scheme will be completed and announced as the international standard. Upon completion, the standard will replace the conventional scheme based on ISO 6983, so-called M&G codes. Further, the new interface scheme will impact the CAD-CAM-CNC process chain and the advancement of the CNC controller. This paper develops an integrated STEP-compliant CNC system (or STEP-CNC) based on the new interface scheme. The system is composed of five modules: (1) Shop Floor Programming System (PosSFP), (2) Tool Path Generator (PosTPG), (3) Tool Path Viewer (PosTPV), (4) Man Machine Interface (PosMMI), and (5) CNC Kernel (PosCNC). The developed system is a prototype but very comprehensive, including all the modules required for realizing “art-to-part” through the new CAD-CAM-CNC chain. Architecture and functional details are presented together with a realistic demonstration.

IT tools to improve the performance of metalworking SMEs

The small manufacturing enterprise is typically recognized as a company that is heavily reliant on its human constituents, namely the skilled manufacturing operators who accept a high level of responsibility for the parts they produce, and also have a major influence on the existence of the company. The significant reduction in costs of IT technology and software tools over recent years has enabled the SME to use hardware and software systems that were previously only available to larger companies. This paper investigates the use of modern IT tools and their application within a metalworking SME. The work is based on a number of major research areas, namely the holonic manufacturing paradigm, distributed planning and control, and open controllers for CNC control. The major emphasis of the paper is the design of appropriate IT tools tailored for the requirements of 'human-centred manufacturing systems' based on holonic concepts to support an autonomous cooperative working environment.

Optimized CNC end-milling: A practical approach

This work proposes and implements a solution to achieve integrated product development that is seamlessly interfaced with optimized CNC end milling. The proposed solution is accurate and general and uses innovative techniques that are new to the field of metal-cutting modelling, simulation and optimization. In addition, the proposed solution is practical and its implementation can be easily and rapidly transferred to industry. First, the current work uses a novel and generic methodology for modelling the geometric aspect of the milling process. Second, techniques from artificial intelligence are introduced to model and optimize the milling process. Next, CAD/CAM and standard engineering development tools are adopted as the implementation tools and platform, and industry and CAD/CAM standards are used as the representations and standards in the development. Finally, the CAD/CAM platform is seamlessly interfaced with CNC production through the development of post-processors for typical CNC controllers found in industry. The system is demonstrated and verified for a typical industrial machining scenario, namely Pocket milling. The results demonstrate the system validity, applicability and accuracy.

Geometric error measurement of spiral bevel gears using a virtual gear model for STEP-NC

Geometric error measurement is required to evaluate the grade of the manufactured gears. Due to the complexity of the spiral bevel gear, direct measurement with the physical part has been conducted in a very limited way. In this paper, we present an indirect measurement based on the virtual gears model (VGM), obtained by NUBS fitting of the surface points measured by CMM (coordinate measuring machine). By comparing the VGM with CAD model (soft-master model), various errors such as tooth profile error and tooth trace error can be automatically measured. The developed method is simple and robust without requiring a special measuring device, and hence it can be applied for the industrial practice as a means for measuring the tooth profile and tooth trace errors which cannot be measured by the conventional method. Further, the model-based method can be incorporated on the advanced CNC controller based on the new CAM–CNC interface scheme of STEP-NC [STEP (standard for transfer and exchange of product model data) based data model for CAM and CNC interface] as an on-line inspection module. Algorithmic details together with experimental validation results are given.

The intelligent on-line monitoring of end milling

The main topics discussed in this paper include sensor integration, data extraction, data processing, monitoring the cutting tool, safety of the tool machinery, and quality of the components in processing. The detection method used in this paper is to extract the workload of a spindle motor from a CNC controller, and then transmit the data via a I/O card for further processing. The computer is connected to the CNC by DNC and is able to detect abnormal conditions and transmit, through DNC, to CNC the NC program to stop the machine or to replace the cutting tool. The systematic architectural instrument develops tools with object-oriented professional software and establishes software structure using a visual component library. The software component structure is made easy for maintaining and extending programs and for the operating system with its graphics user interface.

Minimization of blocking time in component-based software architecture for control systems

In this paper, the architecture of Port-Interface Component Architecture for Real-time system Design (PICARD) is briefly introduced. PICARD is a software architecture and environment for rapid development of application control systems using pre-compiled software components. When a control task has to run at a high frequency, its maximum blocking time should be minimized. Because components are developed and compiled separately, it is not easy to apply traditional methods to reduce blocking time. Two methods are proposed for PICARD to reduce the maximum blocking time. These methods are efficient and easy to implement. PICARD is successfully applied to build a CNC controller, and its real-time characteristics is analyzed.