In the domain of manufacturing, computer numerically controllers (CNC) technology is a major contributor to the production capacity of the enterprises. The advances in CNC technology coupled with enhancements in computing systems have provided the basis to re-examine the way in which computer-aided systems (CAx) can be used to enable global manufacturing. Interoperability of the various components of the CAx chain is therefore a major prerequisite for manufacturing enterprises for becoming strategically agile and consequently globally competitive. Being interoperable, resources can be utilized interchangeably in a plug-and-produce manner. Over the last 8 years the eminence of a STEP standard for machining entitled STEP-NC (numerical control) has become a well-known vehicle for research to improve the level of information availability at the CNC machine tool. In this paper, the authors introduce the background to the evolution of CNC manufacturing over the last 50 years and the current standards available for programming. A review of the literature in interoperable CNC manufacturing is then provided relating to milling, turn-mill and other NC processes. The major part of the paper provides a strategic view of how interoperability can be implemented across the CAx chain with a range of standards used to regulate the flow of information. Finally, the paper outlines the advantages and major issues for future developments in interoperability, identifying future key requirements and limiting factors.

Strategic advantages of interoperability for global manufacturing using CNC technology

Tight quality requirements and stringent customer demands are the main thrust behind the development of new generation machine tool controllers that are more universal, adaptable and interoperable. The development of some international standards such as STEP and STEP-NC presents a vision for intelligent CNC machining. Implementation of STEP-NC enabled Machine Condition Monitoring (MCM) is presented in this paper. The system allows optimisation during machining in order to shorten machining time and increase product quality. In the system, an optiSTEP-NC, an AECopt controller and a Knowledge-Based Evaluation (KBE) module have been developed. The aim of the optiSTEP-NC system is to perform initial feed-rate optimisation based on STEP-NC data to assist process planners in assigning appropriate machining parameters. AECopt acts as a connector between the process planner and machining environment with the intention to provide adaptive and automatic in-process machining optimisation. KBE based-MTConnect is responsible for obtaining machining know-how. Optimisation is performed before, during or after machining operations, based on the data collected and monitored such as machining vibration, acceleration and jerk, cutting power and feed-rate.

Advanced CNC system with in-process feed-rate optimisation

Computer numerical controlled (CNC) machines play an important role in the production capacity of manufacturing enterprises. With the advance of computing technology, computer-aided systems (CAx) have been intensively used together with the CNC machines. The information flow from CAx to CNC machines is unidirectional, due to the widespread use of G&M codes to programme the CNC machines and the mechanism of the generation of part programmes. The CNC machines at the shopfloor have been isolated from the CAx chain. There is no automatic way to capture and feedback the shopfloor knowledge. Reusing shopfloor process knowledge offers the enterprises opportunities to improve manufacturing quality and control while enabling savings in cost and time. Rapid product development relies heavily on quick and reliable process planning and knowledge reuse to facilitate the process plan efficiently and effectively. In this research, the process comprehension approach has been utilised to capture the process knowledge at t...

Process comprehension for shopfloor manufacturing knowledge reuse

Most manufacturing enterprises now employ compute numerical control (CNC) technology in their production chain. Improving the performance and flexibility of the computer aided design (CAD)/computer aided manufacturing (CAM)/CNC chain can therefore, have a significant effect on the competitiveness of such enterprises. Whereas hardware capabilities of these systems have increased proactively over the last few decades, the software components have been updated reactively to support the enhancements found on the newer generation of CNC machines. This passive approach has led to severe incompatibilities between the various CAD/CAM/CNC solutions. This paper presents the impediments and issues arising from such incompatibilities and proposes a new framework to overcome these barriers in achieving interoperability in the CAD/CAM/CNC chain. In the suggested framework different components of the CAD/CAM/CNC chain can exchange information with one another regardless of their native standards. The different elements comprising the framework are demonstrated by utilizing a test component in a dynamic manufacturing scenario.

Toward interoperable CNC manufacturing

The use of adaptive feed rates shortens machining time and increases the potential of efficient machining. Currently, feed rates in an numerically controlled (NC) program are pre-set constant values that are often determined based on the job shop experiences gained over the years by skilled operators. There is no such way to adapt feed rate to on-going cutting conditions since the feed rate is set before the NC code is executed. In this study, an optimizer for canonical machining commands (optiCMC) has been developed. Fuzzy adaptive control is used to keep a constant cutting load by adjusting feed rate automatically to the cutting conditions. The results showed that optimum feed rates can be achieved and controlled during the machining process considering the machine tool's capabilities and limitations. The developed optiCMC helps achieve machining optimization, shorten machining time, and increase product quality.

Adaptive execution of an NC program with feed rate optimization

NC program interpreting is one of the most important tasks of CNC in machine tool system. The existing CNC systems only support vendor-specific NC program input, which restrict the applying of other similar functional NC programs with different program format. Especially for those users owning several machine tools with different CNC from the same provider, the diversity of NC programs dramatically increases their cost and time on operator training and machine tool maintenance. In order to deal with the variety of NC program, an intelligent NC program processor (NCPP) is proposed in this paper. The proposed NCPP has a novel structure with separated NC specification dictionary and processing engine, which ease the CNC system to adapt to a new NC program specification by only updating the NC specification dictionary (NCSD). This paper explains the NC specification dictionary structure by using EBNF representation, which is further implemented in tool command language, an embedded script language tool. Meanwhile, the unchanged processing engine has been designed from a compiler's point of view to process the data dictionary. A NCPP prototype is built to evaluate the proposed design. Case study shows that the proposed NCPP handles different NC program inputs successfully.

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An intelligent NC program processor for CNC system of machine tool

NC program processing plays a vital role in CNC machining. Existing CNC systems support only CNC builder-specific NC program input and this limits the potential application of many NC programs that have the same functions with different formats. In order to manage the variety of NC programs available, a universal NC program processor was developed that can accept and process any kind of NC program. This processor consists of two main components: the first is an NC dictionary, which is generated by an NC specification dictionary generator from the corresponding NC specification, and the second is an interpreting engine, which checks the different input NC programs and generates canonical machining functions in terms of the NC specification dictionary and the canonical machining function library. Finally, a prototype system is built to evaluate the proposed design followed by a successful case study.

A study of a universal NC program processor for a CNC system

Relative movement in X, Y and Z axis directions is made between a main spindle and a table 6 for application in a machine tool in which a work is machined. An emitting element 12 for irradiating laser beam 11 and a photosensitive element 13 are disposed on the table 6. A measuring tool 8 with its top end being shaped as a cone form is attached to the main spindle 4. The laser beam 11 is interrupted with the cone form portion 15 of the measuring tool 8 through relative movement between the table 6 and measuring tool 8 before and after machining a work. Detection signal of interruption is generated at the moment of interruption, position is detected, operation processing is performed so that difference in X, Y and Z axes before and after machining is obtained along with values for correction. Positional coordinate values for three axis directions are detected simultaneously with a measuring device of a simple constitution by use of laser beam and values for correction such as of thermal displacement is obtained by operation processing of displacement values.

Method for controlling a machine tool and apparatus therefor

In this paper, an event-driven simulation method is proposed for the motor driver in a virtual machine tool system (VMT), of which simulation speed is always a puzzle. This method utilizes a set of pre-defined events to trigger the execution of simulator in a non-deterministic manner and at the most efficient moment. Comparing to the conventional time domain simulation method, it dramatically reduces the CPU time consumption without losing simulation accuracy, therefore it improves the simulation efficiency. The effectiveness of this method is verified through a PMSM (Permanent Magnet Synchronous Motor) motor driver model in studying Servo/Mechanical interaction within a VMT.

An event-driven simulation method for motor driver in virtual machine tool system

PROBLEM TO BE SOLVED: To provide a measuring device with a laser beam which is simply formed and can simultaneously detect an axial positional coordinate value of an NC machine tool, and calculate and process a displacement value to obtain a correction value for thermal displacement. SOLUTION: Relative movement in X, Y and Z axis directions is performed between a rotating spindle 4 and a table 6 for application in a machine tool in which a workpiece is machined. A light emitting element 12 for emitting a laser beam 11 and a light receiving element 13 are disposed on the table 6. A measuring tool 8 with the top end thereof shaped as a cone form is attached to the rotating spindle 4. The laser beam 11 is interrupted by a cone form 15 of the measuring tool 8 by the relative movement between the table 6 and the measuring tool 8 before and after machining a workpiece. A skip signal is sent during the interruption, the position is detected and calculated, and the difference of a workpiece in each of an X, Y, and Z axis before and after the machining is calculated to obtain the correction value. COPYRIGHT: (C)2010,JPO&INPIT

Keizo Kashihara

Papers

An intelligent NC program processor for CNC system of machine tool

A study of a universal NC program processor for a CNC system

Method for controlling a machine tool and apparatus therefor

An event-driven simulation method for motor driver in virtual machine tool system

Position measuring method of machine tool and its device