Development of Automated Fixture Planning Systems

Fixturing is an important manufacturing activity. The computeraided fixture design technique is being rapidly developed to reduce the lead time involved in manufacturing planning. An automated fixture configuration design system has been developed to select automatically modular fixture components and place them in position with satisfactory assembly relationships In this paper, an automated fixturing planning system is presented in which fixturing surfaces and points are automatically determined based on workpiece geometry and operational information. Fixturing surface accessibility, feature accuracy, and fixturing stability are the main concerns in the fixture planning. The system development, the fixture planning decision procedure, and an implementation example are presented in the paper.     

Experimental investigation of the performance of a reconfigurable fixturing system

A reconfigurable fixturing system has been developed for computer-integrated assembly environments. The fixturing system employs a number of fixture modules that are set-up, adjusted and changed automatically by the assembly robot without human intervention. A commercially available computer-aided design (CAD) package with the help of a dedicated software program is used for the design, analysis, and verification of the fixture layout. The robot program for setting-up, adjusting, and dismantling the designed fixture is generated automatically. This paper presents and discusses the accuracy of such a reconfigurable fixturing system in view of the off-line programming techniques. The experimental techniques to measure the accuracy and repeatability for setting-up the fixture are presented. The measured results of the robot positioning various types of locating fixture modules are presented and compared with the intended position settings. From the comparison, the accuracy that is to be expected from such an approach to fixturing and measures for improvement are discussed. The cycle times involved in setting-up the fixture modules are also presented and analysed. These results provide an initial guide for manufacturing industries interested in employing such systems in their computer-integrated assembly environment.     

An investigation of an expert system for shearing cut progressive die design

The purpose of this paper is to develop an expert system for shearing cut progressive die, with the aim of enhancing the design of shearing cut progressive dies. This study is different from previous research on shearing cut die design by the author in that the design of one station was extended into a progressive die design. The major research objectives achieved in this study can be summarised as follows:

1. This study presents a pattern recognition method called the new combined structural approach to let the user interpret blanks by a better and more direct method, thereby achieving the goal of communicating with this expert system.
2. The layout of the strip can affect the material cost shared by the press-worked pieces. This study presents the near optimal method for seeing a better layout of the strip in order to save material.
3. Owing to the great variety of blank shapes which cause the variations in pressing procedures, this study proposes a matching combination learning method, which is a learning conscious system for pressing procedures, in order to obtain the optimal number of operation stations in shearing cut progressive die design.
4. The establishment of the knowledge-base system for shearing cut progressive die should improve the efficiency for die design problems.

     

A fuzzy-nets tool-breakage detection system for end-milling operations

This paper describes a new approach, the fuzzy-nets system, for monitoring tool breakage in end-milling operations. The fuzzy-nets tool-breakage detection (FNTBD) system has a self-learning capability to generate rule bases and to fine tune the term sets of each linguistic variable to the appropriate level of granularity. A self-learning algorithm for developing the FNTBD system consists of five steps:

1. Divide the input space into fuzzy regions.
2. Generate fuzzy rules from given data pairs through experimentation.
3. Avoid conflicting rules based on top-down or bottom-up methodologies.
4. Develop a combined fuzzy rule base.
5. Determine a mapping system based on the fuzzy rule base.

Learning is accomplished by fine-tuning the parameters in the fuzzy-nets system within the on-line learning capability. Following establishment of the rule base, the performance of the FNTBD system is examined for an end-milling operation. It was observed and verified experimentally that this new FNTBD approach can successfully detect tool breakage in end-milling operations.     

Optimizing the fuzzy-nets training scheme using the Taguchi parameter design

Fuzzy nets have been proposed to combine the learning ability of neural networks and the reasoning ability of fuzzy logic to deal with complex control systems. This paper presents a systematic way of identifying the significant factors and optimising the performance of a fuzzy-nets application. To present the methodology, a model of a truck backing up has been evaluated. Four factors were considered:

1. The number of training sets.
2. The number of fuzzy regions.
3. The membership functions.
4. The fuzzy reasoning methods which would affect the performance of the fuzzy-nets training scheme in nonlinear applications.

The Taguchi parameter design was implemented with anL ₉ (3⁴) orthogonal array to identify the optimal combination for training consideration. Both raw and signal-to-noise (S/N) ratios were evaluated to identify the optimal combination for the performance of fuzzy-nets training with very limited variation. The performance of the proposed fuzzy-nets scheme for the model of the truck backing up was represented by the average errors between the truck and loading dock: 0.178 units and 0.204 degrees. The results demonstrate that the Taguchi parameter design is a robust approach for optimising the performance of the fuzzy-nets training scheme.     

FLEXIBLE ASSEMBLY FIXTURING LAYOUT MODELING AND OPTIMIZATION BASED ON GENETIC ALGORITHM

There are many welding fixture layout design problems of flexible parts in body-in-white assembly process, which directly cause body assemble variation. The fixture layout design quality is mainly influenced by the position and quantity of fixture locators and clamps. A general analysis model of flexible assembles deformation caused by fixture is set up based on "N-2-1" locating principle, in which the locator and clamper are treated as the same fixture layout elements. An analysis model for the flexible part deformation in fixturing is set up in order to obtain the optimization object function and constraints accordingly. The final fixture element layout could be obtained through global optimal research by using improved genetic algorithm, which effectively decreases fixture elements layout influence on flexible assembles deformation.     

A systematic conceptual design of modular fixtures

The replacement of dedicated fixtures by modular fixturing systems seems to be a trend in the manufacturing field, especially in meeting the desire for greater flexibility but the selection of appropriate modules from a modular fixturing system and subsequent assembly is itself not an easy task. This research provides a systematic design method to help dedicated fixture users to convert to modular fixturing system users. This method classifies modules into five functional groups and then selects proper modules from each group in accordance with the functional request of the fixture assembly. This systematic design of modular fixtures helps a dedicated fixture user to build an economical and efficient modular fixturing system.     

The development of an object-oriented Petri net cell control model

This paper presents an object-oriented Petri net cell control (OPNCC) model for scheduling and controlling the operations of a flexible manufacturing cell. The development of the OPNCC model includes three phases:

1. Static analysis.
2. Dynamic analysis.
3. Integration.

The dynamic analysis, the most important phase in developing the OPNCC model, will first construct the object-oriented Petri net (OPN) for each physical object and connect all the related “encapsulated” OPNs to be a complete OPN model to represent the dynamic behaviour or control logic of shop floor operations. Then, the control logic of the complete OPN model must be analysed through an object behaviour analysis, an inter-object message passing analysis and a conflict analysis. The OPNCC model not only possesses the characteristics of object-oriented method (e.g. inheritance, encapsulation and a higher degree of flexibility and reusability) and Petri nets (e.g. graphical representation and mathematical analysis capabilities), but also incorporates scheduling/dispatching knowledge in the control logic specified by the OPN model. The practical significance of the OPNCC model is that practitioners may apply it to develop both a real-time cell controller and an off-line shop floor scheduling simulator.     

A literature survey of fixturedesign automation

This paper gives a review of fixture-design research, most of it done in the 1980s. The major topics of the review are the fixturing principles (supporting, locating and clamping), automated fixture design (configuration, assembly and verification), and fixture hardware design (dedicated, modular and electric/magnetic types).     

孔系组合夹具三维构形自动生成研究

采用ObjectARX语言开发了具有夹具特征和装配特征的参数化的孔系组合夹具元件库,并基于夹具特征和专家系统,建立了一种自动确定定位和夹紧区域的孔系组合夹具构形图自动生成系统,并阐述了有关算法主要思想.     

Manipulators: Execution of prescribed trajectories special link positions and versions of assembly

A new technique for the kinematical analysis and design of manipulators based on the following principles is proposed:

• 1.(1) Link positions are determined by subsystems of equations which contain a reduced number of unknowns and may be solved separately. The derivation of such systems of equations may be based: (a) on the modeling of the manipulator by two open chains or (b) on modified closure matrix equations.
• 2.(2) Special 4 × 4 matrices which describe separately the link geometry and the relative motion of links are applied.
• 3.(3) All potential configurations which are formed by the manipulator links may be determined using the information on special link positions.
• 4.(4) Angles of rotation in the joints are determined as functions of the trajectory parameters using a system of six nonlinear equations represented in echelon shape.

The above techniques are applied for the kinematical analysis of a Cincinnati Milacron T3 manipulator with six degrees-of-freedom. A computer program for the control of rotations in the joints has been developed based on these techniques, and the results are presented at the end of this paper.     

Selection of preliminary locating and clamping positions on a workpiece for an automatic fixture design system

This paper focuses on the development of heuristic algorithms for selecting the locating and clamping positions on an automatic fixture configuration for a given workpiece for an automatic fixture design (AFD) system. It discusses several issues regarding (i) an informationally complete product model, and (ii) the development of necessary computational modules coupled with a knowledge based system to reason about the workpiece's geometric characteristics for determining the locating and clamping positions. The motivation of the work is to develop a fixturing subsystem as an integral part of the complete CIM environment. A prototype AFD system has been completed in the object oriented programming platform of Wisdom's Concept Modeller. It has used several geometric reasoning mechanisms based on the traditional fixture design principles, and on the principles of collision-free assembly. The system exploits the power of Wisdom's advanced geometric modelling (AGM), and it implements the basic architecture of the proposed knowledge based fixture design system.     

The application of the simulated annealing method and heuristic algorithms in the selection of fixture elements

This paper deals with the selection of suitable fixture element combinations and fixture allocation for a workpiece to allow for the different positions of the fixturing points, which are already given based on related theories. The advanced modelling extension (AME) of AutoCAD R12 was used as the 3D graphic interface. The function suitable for the AME environment was also controlled to obtain detailed data of the workpiece.First of all, the concept of group technology (GT) was used to categorise and encode the modular fixture elements with similar functions for cutting purposes. Next, the AME was combined with API (application programming interface) and Autolisp to establish the graphic illustration system for fixture elements. Then different heuristic algorithms for fixture element selection were developed to correspond to different requirements in fixture functions. The required fixture elements were then selected with the help of the simulated annealing calculation method to derive a suitable and economical number of fixture element combinations. The height of the fixture element combination derived may not match the height of the fixture point originally located. The workpiece shape also affects the allocated position of the fixture elements. Therefore, a number of heuristic algorithms were developed in this study to process all the factors involved and to obtain a desirable selection for fixture elements.     

计算机辅助夹具设计系统SEFDS的开发与研制

本文介绍了由作者开发的计算机夹具设计SEFDS系统软件,该系统工作在IBM-PC/XT或其兼容机上,其程序语言是Auto CAD软件。系统中建立了机床夹具的各种标准件,包括支承件、定位件、导向件、紧固件等数据库及其图形库和有关的图块,具有能在图上自动标注尺寸、公差、表面粗糙度、形位公差的功能。在设计夹具时,SEFDS系统在计算机屏幕上提供交互式菜单,通过人机对话,自动生成夹具的装配图和零件图,由绘图机或打印机输出图形,作图准确、迅速,有实用价值。     

Machining Fixture Verification for Nonlinear Fixture Systems

This paper presents a fixture configuration verification methodology for nonlinear fixture systems, which is developed on the basis of optimal clamping forces and total restraint. This method can be applied for validating the feasibility of a fixture with point, line and area contacts in two stages: fixturing and machining. The "∞-∞-∞" principle for nonlinear fixture location is proposed. The automatic fixture verification system is modelled as a nonlinear optimisation problem with respect to minimum clamping forces. The method provides a simple and effective means for: (a) verifying whether a particular fixturing configuration is valid with respect to locating stability, deterministic workpiece location, clamping stability and total restraint and (b) determining minimum variable clamping forces over the entire machining time. Two case studies are presented to demonstrate the effectiveness and the capabilities of the methodology. ID="A1"Correspondance and offprint requests to: Prof. D. R. Strong, Department of Mechanical and Industrial Engineering, The University of Manitoba, Winnipeg, Manitoba, Canada R3T 5V6. E-mail: strong@ms.umanitoba.ca     

Velocity fields within sewers: An experimental study

Measuring the flow rate through sewer networks is necessary for a number of reasons. To achieve such measurements, precise knowledge of the hydrodynamic conditions of each potential measurement location proves critical. A research project is currently being conducted to improve the representativeness of flow rate measurements recorded in man-entry sewers. Three objectives are being pursued as part of this project:

• ∘assisting with the selection of a suitable measurement section;
• ∘designing for proper sensor implementation in a given section; and
• ∘setting up an appropriate system for processing the raw data provided by sensors.

This project relies upon numerical simulations; moreover, experimental devices have been developed and utilized to collect measurement data for purposes of model validation. This paper will describe such experimental devices and presents the results obtained after several months of investigation.     

Effects of display type, speed, and text/background colour-combination of dynamic display on users' comprehension for dual-task in reading static and dynamic display information

In the research carried out, a display environment containing both a static and a dynamic section was designed to investigate the effects of the design factors of the dynamic display on users' e-reading comprehension performance in the static and dynamic sections. The dynamic display factors include:

1. Display types (leading, RSVP, and flash),
2. Speeds [140, 195, 250, and 305 words per minute (wpm)], and
3. Text/background colour-combinations (16 colour-combination settings).

Experimental results showed that subjects' comprehension on static display mode was not significantly affected by any of the dynamic display factors. Nevertheless, all the dynamic display factors had significant effects on subjects' comprehension of the information in the dynamic display section. With the leading display type, subjects performed best at 195 wpm. When the display type was RSVP or flash, subjects performed best at 140 wpm and worst at both 250 and 305 wpm. The effects of the text/background colour-combinations were that subjects performed the best comprehension at the dynamic display section with the same text/background colour-combinations of the static display sections. The dynamic display section with the same text/background colours but with opposite display polarities of the static display sections was second. Subjects performed the worst comprehension when the text/background colours of the dynamic display section were completely different from that of the static display section.     

Computer-Aided Fixture Design Verification. Part 1. The Framework and Modelling

Computer-aided fixture design (CAFD) techniques have been advanced rapidly so that fixture configurations can be generated automatically, for both modular fixtures and dedicated fixtures. Computer-aided fixture design verification (CAFDV) is the technique for verifying and improving existing fixture designs. In this paper, the framework of CAFDV is introduced based on two models, i.e., geometric and kinematic models. The fixturing tolerance and stability verification will be presented in separate papers.     

Computer-Aided Fixture Design Verification. Part 3. Stability Analysis

In fixture design, a workpiece is required to remain stable throughout the fixturing and machining processes in order to achieve safety and machining accuracy. This requirement is verified by a function of the computer-aided fixture design verification (CAFDV) system. This paper presents the methodologies of fixturing stability analysis in CAFDV. A kinetic fixture model is created to formulate the stability problem, and a fixture stiffness matrix (FSM) is derived to solve the problem. This approach not only verifies fixturing stability, but also finds the minimum clamping forces, fixture deformation, and fixture reaction forces. The clamping sequence can also be verified with this approach.     

Application of microcomputer for assessing the probe lobing error and geometric errors of CMMs using commercial ring gauges

Performance verification and frequent reverification of working accuracy of coordinate measuring machines are currently acknowledged as essential operational processes. In this paper, an efficient microcomputer based method has been proposed for the accuracy assessment of the CMMs of CNC type based on the probing of commercially available ring gauges. The geometric inaccuracy data of the ring gauges are measured, stored, and thus can be used as a transfer standard. A computer module for measurement-path generation has been developed, with which automatic CNC measurement codes can be generated for specific CMMs. The ring gauges are measured on the CMMs, and the measured data are feedback to the PC. For the error analysis, a new error analysis module has been developed for performance checking of a measurement probe, where the direction-dependent probe lobing error can be successfully evaluated. A least-squares-based approach has been implemented, with which the scale errors and the squareness error can be evaluated simultaneously in the local measurement position. The advantages of the proposed method are:

1. The rapid assessment for the probe lobing error.
2. Simultaneous evaluation of the scale errors and the squareness error.
3. Highly integrated approach for the measurement-error evaluation processes, which are implemented via a PC.

Practical CMMs have been chosen and the accuracy assessment is performed, demonstrating the high efficiency of the developed system. The developed method can be applied to performance verification or day-to-day reverification of CMMs of CNC type.