Automated Fixture Design Research Articles

A study on automatic fixture design using reinforcement learning

Fixtures are used to locate and secure workpieces for further machining or measurement process. Design of these fixtures remains a costly process due to the significant technical know-how required. Automated fixture design can mitigate much of these costs by reducing the dependence on skilled labour, making it an attractive endeavour. Historical attempts in achieving automated fixture design solutions predominantly relied on case-based reasoning (CBR) to generate fixtures by extrapolating from previously proven designs. These approaches are limited by their dependence on a fixturing library. Attempts in using rule-based reasoning (RBR) has also shown to be difficult to implement comprehensively. Reinforcement learning, on the other hand, does not require a fixturing library and instead builds experience and learns through interacting with an environment. This paper discusses the use of reinforcement learning to generate optimized fixturing solutions. Through a proposed reinforcement learning driven fixture design (RL-FD) framework, reinforcement learning was used to generate optimized fixturing solutions. In response to the fixturing environment, adjustments to the reinforcement learning process in the exploration phase is studied. A case study is presented, comparing a conventional exploration method with an adjusted one. Both agents show improved average results over time, with the adjusted exploration model exhibiting faster performance.

Automated Fixture Design using an Imprint-based Design Approach and Optimisation in Simulation

Object aligning and holding fixtures for robotic assembly tasks are important in industry in order to successfully complete an assembly. However, the designing of a fixture is usually done manually which can be a long and tedious process including many iterations, even for experienced engineers. This paper presents a method to design fixtures automatically for use in robotic assemblies and pick-and-place tasks. To achieve this, a new automated method to design the cut-out for a fixture is introduced. The method uses a parameterized version of the object's imprint to design the cut-out. The fixtures generated using this method are optimized in simulations to determine their final parameters for a specific application. Dynamic simulations are used to evaluate each iteration of the cut-out. Lastly, the method is applied to a use-case from the industry to design a fixture for use in a robotic assembly task.

A workpiece stability-based iterative planning of clamping forces for fixturing layout specification of a complex workpiece

When a workpiece is reasonably located on a machine bed, it will be subject to gravity and cutting forces in the machining process. In order to prevent them from causing the position variation and the production accident, it is important to determine clamping forces for workpiece stability. In this paper, the workpiece stability is categorized into the force existence for the unknown clamping forces and the force feasibility for the given clamping forces. A linear programming technology is suggested to verify the force existence and the force feasibility at the corresponding clamping point. And then, the clamping surface is discretized into a node set for one clamping force. At every node with the force existence, the magnitude of clamping force can be obtained by the “1-clamping force” iterative planning algorithm in which the step will generally decrease with the difference of the force existences between two adjacent clamping forces until it is no more than the threshold value. Moreover, the workpiece is frequently hold by n clamping forces which can equivalently be described as a function of one polar radius and n-1 polar angles. Thus, “n-clamping force” iterative planning algorithm can be established to solve the polar radius by calling the 1-clamping force iterative planning algorithm. Finally, the n-clamping force iterative planning algorithm is used to obtain double clamping forces. The maximum relative errors of placements and magnitudes are 0.145% and 0.151% in comparison with the results of the analytic method, respectively. Again, a third typical fixturing layout is used to validated 1-clamping force iterative planning algorithm with the relative errors within 0.770%. Because the proposed method transforms the continuous design problem of clamping forces into the discrete analysis problem of workpiece stability, it can not only apply to the complex workpiece but also benefit the development of automated fixture design.

Computer aided fixture design - A case based approach

Automated fixture design plays important role in process planning and integration of CAD and CAM. An automated fixture setup design system is developed where when fixturing surfaces and points are described allowing modular fixture components to get automatically select for generating fixture units and placed into position with satisfying assembled conditions. In past, various knowledge based system have been developed to implement CAFD in practice. In this paper, to obtain an acceptable automated machining fixture design, a case-based reasoning method with developed retrieval system is proposed. Visual Basic (VB) programming language is used in integrating with SolidWorks API (Application programming interface) module for better retrieval procedure reducing computational time. These properties are incorporated in numerical simulation to determine the best fit for practical use.

Design for Automation: The Rapid Fixture Approach

As product varieties rise and lifecycles shorten, development approaches need to be adapted. Current trends aiming to solve the dissonance of reduced time to market and increased product variety include agile methods. In this context not only product design processes need to be adapted but also development of production processes and manufacturing equipment. At the example of fixture design, this paper presents an approach which allows an agile provision as well as a reconfiguration of equipment. The solution presented consists of a fixture design concept consisting of design rules which allow implementation into a tool for automated fixture design.

Fixture Design Automation and Optimization Techniques: Review and Future Trends

Fixture design is crucial part of manufacturing process. Fixture design is a critical design activity process, in which automation plays an integral role in linking computer-aided design (CAD) and computer-aided manufacturing (CAD). This paper presents a literature review in computer aided fixture design (CAFD) in terms of automation and optimization techniques over the past decades. First, the reason behind necessity of automated fixture design is stated. According to the degree of automation, fixture design methods are then categorized based on significant work done in the CAFD field. Regarding the need of automated fixture design systems, optimization techniques, which are mostly used for automated CAFD methods, are closely considered. The significant optimization techniques works are then studied in case of applications and working principle. At the end, the current weaknesses of the existing methods and the research fields, which require deeper studies as future trends, are presented as well.

A pilot framework developed as a common platform integrating diverse elements of computer aided fixture design

In the present study, an integrated computer-aided engineering platform has been developed for fixture design. Different computer aids needed for an automated fixture design system include geometrical modelling, finite element analysis, specialised mathematical tools, such as screw theory, and also artificial intelligence routines. It has been illustrated through several examples that the Python environment is a capable candidate to be employed for developing an integrated platform capable of providing these computer-aided tools. For this purpose, different specialised modules were developed, including a CAD system for geometrical modelling of workpiece, a mathematical analysis module for designing the locating system by using the screw theory, a FEM module being employed for support system design and an expert fixture planning module. The developed platform has also been examined for its capability to be interfaced with existing commercial CAD, FEM and expert system programmes.

Design-to-fabrication automation for the cognitive machine shop

To meet the rising demands for pure customization of products, new approaches for automated fabrication of customized part geometry are needed, on both the software and hardware side, that balance flexibility, robustness and efficiency. This is a great challenge since today it requires significant human expertise supported, only partially, by computer-aided approaches. This paper introduces a new approach and framework for an autonomous design-to-fabrication system that integrates cognitive capabilities, such as reasoning from knowledge models and autonomous planning, and embeds these in the machines themselves to automatically fabricate customized parts. The framework integrates into a common process automatic workpiece selection using an ontology, generative CNC machining planning using shape grammars and automated fixture design, based on a novel flexible fixture device hardware. Initial results are given for the machining planning approach applied to 2.5D parts with a defined approach direction and the prototyped fixture device is presented. The advantages and potential of the framework stem mainly from applying the principles of cognitive technical systems to a fabrication system to develop an integrated and on-line approach. The methods are developed specifically for use on the machine shop floor to take advantage of the possibility to update and extend knowledge models to reflect current fabrication capabilities and to adapt to changes in the environment and re-plan during operation. Finally, future directions, including integrating on-line perception and learning, are discussed, which are required to create a truly flexible and cognitive fabrication system.

Automated fixture design for a rapid machining process

PurposeThe purpose of this paper is to present a methodology for the automated design of a fixturing system for a rapid machining process.Design/methodology/approachThe method proposed is the use of sacrificial fixturing, similar to the support structures in existing rapid prototyping (RP) processes. During the machining process, sacrificial supports emerge incrementally and, at the end of the process, are the only entities connecting the part to the remaining stock material.FindingsThe support design methods have been shown to be extremely flexible in securing a variety of complex parts with relatively tight part tolerances using a rapid machining process.Research limitations/implicationsThe automated design of support structures is currently relegated to use in a CNC rapid prototyping process that uses a fourth axis for rotary setups.Practical implicationsThe methods used here make rapid machining feasible, as it solves the daunting problem of automated fixturing.Originality/valueThe paper proposes an innovative solution for an automatic fixturing system in subtractive RP.

Optimizing workholding efficiency through fixture function simulation

In the past two decades, simulating workpiece–fixture interactions has remarkably drawn the attention of academia. However, many aspects of the workpiece–fixture system, specifically workpiece–fixture contact condition, still enjoy research effort. For the efficient use of Automated Fixture Design (AFD) systems, verification of their outputs is required. This paper presents a workholding simulation approach that considers assessment of AFD system outputs regarding different workholding parameters. The effect of friction forces on workholding and part rigid body stability is considered. Besides, determining deformation and stress in the workpiece, locators and clamps are modelled and their elastic deformation and stress distribution are computed. A procedure based on the application of contact elements in finite-element method is developed to quantify the status of contact between the workholding elements and the workpiece. Clamping tightness is modelled and its effect on the workpiece–fixture system performance is quantified. The central component of the verification tool is the use of nonlinear finite-element analysis to model the frictional interactions in workpiece–fixture system.

Computer aided fixture design: Using information intensive function models in the development of automated fixture design systems

In this paper, the development of an Information Intensive Function Model (IIFM) of fixture design activities is discussed. This function model was developed using the IDEF-0 (Integrated Definition) methodology and was built primarily after interacting with expert fixture designers. In addition, knowledge from fixture design, tool design, and metalcutting handbooks and from journal papers was used to lend a holistic flavor to the developed IDEF-0 model. An IDEF-0 modeling software tool, AIO Win®, was used to build this model at various levels of decomposition. This paper also discusses the importance of IIFMs in the current and future design of Computer Aided Fixture Design (CAFD) systems.

Trends and perspectives: Computer aided fixture design: Using information intensive function models in the development of automated fixture design systems: J. Cecil, v21, n1, 2002, pp58–71

Trends and perspectives: Computer aided fixture design: Using information intensive function models in the development of automated fixture design systems: J. Cecil, v21, n1, 2002, pp58–71

A Clamping Design Approach for Automated Fixture Design

in this paper, an innovative clamping design approach is described in the context ofcomputer-aided fixture design activities. The clamping design approach involves identification of clamping surfaces and clamp points on a given workpiece. This approach can be applied in conjunction with a locator design approach to hold and support the workpiece during machining and to position the workpiece correctly with respect to the cutting tool. Detailed steps are given for automated clamp design. Geometric reasoning techniques are used to determine feasible clamp faces and positions. The required inputs include CAD model specifications, features identified on the finished workpiece, locator points and elements.

Fixturing Analysis For Stability Consideration in an Automated Fixture Design System

Stability analysis plays a critical role in determining the applicability of a fixture design. This paper reports the development of a computational methodology for quantitatively analyzing the workpiece’s stability in the automated fixture design (AFD) environment. In stability analysis, the virtual disturbance which is expressed as a wrench in the screw coordinates and has the same tendency as those fixturing and machining forces to destabilize the workpiece is adopted in the study, and the stability of the workpiece is characterized based on its capability to overcome the virtual disturbance. The stability characteristics for each fixturing configuration (i.e., positions for fixturing components of supporters, locators and clamps) itself are obtained from the stability analysis and used in the re-design process to determine the better design of fixturing configuration.

A Fast Interference Checking Algorithm for Automated Fixture Design Verification

Fixtures are tooling devices used to locate, support and hold workpieces during a manufacturing process. The major purpose of a computer-aided fixture design (CAFD) system is to provide a fixture design based on fixturing principles and workpiece information. Interference checking between the machining tool and fixture units, as well as between fixture units, is one of the important functions of automated fixture design. This paper presents a fast interference checking algorithnt for automated modular fixture design validation. It is based on the study of the geometric characteristics of modular fixture components and the machining tool. The fixture component model is simplified into a 2D contour model with height information. The tool-path model is represented by a moving dot for 3-axis operations, or a moving line segment in 5-axis operations, as the fixture component model is expanded according to the tool radius. The method is different from the popular collision detection procedure using swept volume and is more efficient for fixturing verification. Application of this method will greatly reduce the computation complexity for fixturing interference checking. The method is implemented with a CAFD system. An example is given at the end of the paper.

An automated design and assembly of interference-free modular fixture setup

This paper describes an automated modular fixture design system developed using a CAD-based methodology and implemented on a 3-D CAD/CAM software package. The developed automated fixture design (AFD) system automates the fixturing points determination and is integrated on top of the previously developed interactive and semi-automated fixture design systems. The determination of fixturing points is implemented in compliance with the fixturing principles that are formulated as heuristics rules to generate candidate list of points and then select the exact points from the list. Apart from determining the fixturing points automatically, the system is capable of producing cutting tool collision-free fixture design using its machining interference detection sub-module. The machining interference detection is accomplished through the use of cutter swept solid based on cutter swept volume approach. Therefore, using the developed AFD, an interference-free fixture design and assembly can be achieved in the possible shortest design lead-time.

An Integrated Approach to Collision-Free Computer-Aided Modular Fixture Design

This paper describes a CAD-based methodology for developing a modular fixture design system using the Unigraphics (UG) solid modeller, integrated with a modular fixture element database, based on a hole-based IMAO modular fixturing system. A parametric modelling technique has been applied to construct the database. An integrated methodology is introduced in the system in which the functions of interactive, semi-automated and automated fixture design systems are combined collaboratively in a single environment. This provides the flexibility and functionality for making the design process more efficient. The interactive fixture design module helps the designer to select the fixturing faces, points and elements for building a fixture. Semi-automated and automated fixture design modules are built by transforming the designers' experience and knowledge into rules and algorithms to automate the selection of fixturing points and elements, More importantly, the system aims at producing a tool-collision-free fixture design using a machining interference detection submodule based on a cutter swept volume approach.

Fixturing surface accessibility analysis for automated fixture design

Fixturing is an important manufacturing activity in the production cycle. The computer-aided fixture design (CAFD) technique has been developed and become part of CAD/CAM integration. CAFD consists of three major aspects: setup planning, fixture planning, and fixture configuration design. An automated modular fixture configuration design system has been developed and applied to industrial practice. This paper focuses on a technical problem involved in the development of automated fixture planning systems, that is, the accessibility analysis of a fixturing surface on workpiece. The fixturing surface accessibility should be correctly assessed to reflect the extent of ease to place a fixture component in contact with the fixturing surface. The objective of accessibility analysis is to help the fixture planning fulfill the optimum selection of fixturing surfaces and points on workpiece. Firstly, several basic criteria for evaluating the eligibility of a surface being a preliminary candidate fixturing surface are discussed. Secondly, by applying a discretization technique, an accessibility model of fixturing surfaces is established based on an overall evaluation of the accessibility of discrete points on the surface. Finally, the implementation issue and a analysis/ design example are presented.

Geometric reasoning for re-allocation of supporting and clamping positions in the automated fixture design system

Geometric reasoning is an indispensable part of an automated fixture design system. This paper introduces a rational approach based on the use of both qualitative and quantitative reasoning tools to plan for the “best” supporting, locating and clamping positions (on a given workpiece) to hold the workpiece rigidly and accurately during machining processes. It discusses general algorithms to verify the preliminary fixture configuration, as obtained by using 3-2-1 locating rules against workpiece deformation and work piece-tool interference, and to re-allocate the locating positions, if necessary. The paper also addresses the issues of implementing the algorithm in a prototype, automated fixture design system.

Geometric reasoning for re-allocation of supporting and clamping positions in the automated fixture design system

Geometric reasoning is an indispensable part of an automated fixture design system. This paper introduces a rational approach based on the use of both qualitative and quantitative reasoning tools to plan for the “best” supporting, locating and clamping positions (on a given workpiece) to hold the workpiece rigidly and accurately during machining processes. It discusses general algorithms to verify the preliminary fixture configuration, as obtained by using 3-2-1 locating rules against workpiece deformation and workpiece-tool interference, and to re-allocate the locating positions, if necessary. The paper also addresses the issues of implementing the algorithm in a prototype, automated fixture design system.