Suk-Hwan Suh

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

Abstract 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.

On the architecture of intelligent STEP-compliant CNC

STEP-NC or ISO 14649 is a new data model between CAM and CNC, currently under development by ISO TC184 SC1 and 4. Distinguished from the present CNC language (ISO 6983), the new data model includes rich information enabling feature-based programming and control for manufacturing operation. This paper aims to present a conceptual framework for an intelligent STEP-compliant CNC (called ASNC: Autonomous STEP-compliant CNC) taking ISO 14649 as an input and carrying out manufacturing tasks in an intelligent and autonomous manner. The framework is derived from the analysis of information contents of ISO 14649, and the role of CNC on the shop floor of an intelligent manufacturing system. To show the mechanism of ASNC, an operational scenario with functional details for NC milling operation is presented. The scenario illustrates that the new CNC can autonomously carry out the manufacturing tasks based on ISO 14649 and can deal with unexpected changes on the shop floor.

UbiDM: A new paradigm for product design and manufacturing via ubiquitous computing technology

Since ubiquitous technology was introduced in the early 1980s, it has rapidly developed, and been applied to various domains mainly for the improvement of human life. In this article, the authors propose that ubiquitous computing technology can be effectively used for the design and manufacturing of a product by proposing a new paradigm, called UbiDM® (Design and Manufacture via Ubiquitous Computing Technology). The key aspect of UbiDM is the utilisation of the entire product lifecycle information obtained via ubiquitous computing technology for the design and manufacture of the product. The new paradigm can solve many of the problems that have not been properly handled by previous manufacturing paradigms. Specifically, it will address the concept of UbiDM by the following aspects: (1) why there is a need for UbiDM; (2) the essence of UbiDM; (3) enabling technologies; (4) application area; (5) worldwide R&D status; and (6) the societal impacts of UbiDM.

Development of an automatic trajectory planning system (ATPS) for spray painting robots

An automatic trajectory planning system (ATPS) for painting robots is developed. Geometric modeling, painting mechanics, and robot dynamics are considered to produce an optimal trajectory (in the sense of coating uniformity and painting time) based on the CAD data describing the shape of objects. The scheme was implemented on a SUN/4 workstation to develop an ATPS for painting robots. To test the effectiveness and illustrate the developed system, numerous experiments were performed and analyzed. The practical application of the developed system is for planning an optimal robot trajectory such that uniform coating thickness is achieved in minimum painting time.<<ETX>>

Error modelling and measurement for the rotary table of five-axis machine tools

Rotary tables are widely used with multi-axis machine tools as a means for providing rotational motions for the cutting tools on the three-axis machine tools used for five-axis machining operations. In this paper, we present a comprehensive procedure for the calibration of the rotary table including: geometric error model; error compensation method for the CNC controller; error measurement method; and verification of the error model and compensation algorithm with experimental apparatus. The methods developed were verified by various experiments, showing the validity and effectiveness of the presented methods, indicating they can be used for multi-axis machine tools as a means of calibration and precision enhancement of the rotary table.

STEP-compliant CNC system for turning: Data model, architecture, and implementation

STEP-NC, a new data model for CAD-CAM-CNC chain, is expected to encompass the whole scope of e-manufacturing. The new data model formalized as ISO 14649 is under development by ISO TC184 SC1 and SC4 for the replacement of the old standard so-called G&M codes, formalized as ISO 6983 which has been used since the 1950s. As the new data model is being established, development and implementation of STEP-compliant CAD/CAM/CNC system based on the new data model is drawing worldwide attention. Several systems have been reported in such international conventions as the ISO Expert Committee Meeting. Up to the present time, all the STEP-CNC systems are intended for milling operation. In this paper, the authors first present STEP-compliant CNC system for turning system including the data model, followed by a generic architecture and functionality. Implementation results obtained from a prototype system called TurnSTEP have been provided. Based on the results, the authors are convinced of the validity of the STEP-NC data model together with the effectiveness of the STEP-CNC system for turning.

Reincarnation of G-code based part programs into STEP-NC for turning applications

As STEP-NC emerges as the new CNC control method and a fundamental means for realizing e-manufacturing, old manufacturing information based on the conventional manufacturing standard will become obsolete. In practice, replacement of G-code based part programs into STEP-NC is a huge task. In this paper, methods to interpret G-code based part programs into STEP-NC code are investigated. G-code is a compact, coded set of numbers for axis movements, while STEP-NC is very comprehensive and includes information about features, operations, strategies, cutting tools, and so on. It is thus very challenging to derive such comprehensive information from the low level G-code information. In this paper, we first clarify what should be given and what may be given, and then present algorithms for deriving STEP-NC information, such as geometric features, operations, etc., from the tool movement (G-code) based on expert reasoning. The algorithms are developed for the turning application. The developed algorithms were implemented and tested on G-code part programs used in actual practice.

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

Abstract 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.

A comprehensive method for calibration of volumetric positioning accuracy of CNC-machines

AbstractA comprehensive method for measuring the systematic errors of CNC-machine tools has been studied. The method used for measurement and calibration of machine tool errors should be general and efficient. The objectives of this study include:1.Volumetric error modelling.2.Experimental procedure for error measurement.3.A tool position and path compensation method.4.The verification method. Using the same method, the machine tool status can be completely identified and its accuracy can be enhanced by software error compensation. The point compensation method can be used as a means for modifying the nominal tool path and on-the-machine inspection where the machine tool is used as a coordinate measuring machine. The validity of the error calibration method proposed in this paper was shown using a vertical 3-axis CNC machine with a laser interferometer and a ball bar technique.

Incorporation of tool deflection in tool path computation: Simulation and analysis

For geometric accuracy, the problem of tool deflection should be resolved for 2-D finish-cut contour machining. This paper investigates a path correction method for the nominal path given by the part program. The significance of the deflection error is first shown by experiments, and a direct compensation scheme is proposed that evaluates and corrects the tool path based on an instantaneous deflection force model until the desired contour is obtained in the presence of tool deflection in actual machining. The method is distinguished from the previous approach based on geometric and cutting simulation and on feed rate adjustment via adaptive control. Further, the method can be viewed as a direct and active method toward net-shape NC machining. Simulation results show the validity and adequacy of the path-modification scheme under various cutting conditions.