Otto Jan Bakker

Active fixturing: literature review and future research directions

Fixtures are used to fixate, position and support workpieces and represent a crucial tool in manufacturing. Their performance determines the result of the whole manufacturing process of a product. There is a vast amount of research done on automatic fixture layout synthesis and optimisation and fixture design verification. Most of this work considers fixture mechanics to be static and the fixture elements to be passive. However, a new generation of fixtures has emerged that has actuated fixture elements for active control of the part–fixture system during manufacturing operations to increase the end product quality. This paper analyses the latest studies in the field of active fixture design and its relationship with flexible and reconfigurable fixturing systems. First, a brief introduction is given on the importance of research of fixturing systems. Secondly, the basics of workholding and fixture design are visited, after which the state-of-the-art in active fixturing and related concepts is presented. Fourthly, part–fixture dynamics and design strategies which take these into account are discussed. Fifthly, the control strategies used in active fixturing systems are examined. Finally, some final conclusions and prospective future research directions are presented.

Fixture control by hydraulic actuation using a reduced workpiece model

Abstract In this paper the dynamic behaviour of a part and an actuated fixture system is studied. The part is modelled using the finite element method. Subsequently, a reduced model is established using the Craig—Bampton reduction method in order to create a small-sized model, accurately describing the dynamic behaviour of the part. The clampers and locators of the fixture are modelled as springs. The fixture frame is considered to be much stiffer than the locators such that it provides the zero displacement boundary conditions to the locators. A hydraulic actuator is utilized to provide the adaptive clamping forces. A methodology is presented to obtain the reduced model of the part and to couple it with the model of the active fixture. After investigating proportional control, lag, and lead filters for dynamic compensation, the analysis shows that position feedback can be used effectively to minimize unnecessary displacement of the workpiece.

Model-Based Control of An Active Fixture for Advanced Aerospace Components

In this paper the dynamical behaviour of a flexible part and an actively controlled fixture system is studied. Four active clamps are used for the control of the part-fixture system. Advanced finite element (FE) analyses have been carried out to model the part and the adaptive clamps. An accurate small-sized model of the part is established using the Craig—Bampton reduction method. A second-order model has been established for the adaptive clamps on the basis of the FE model. The supports and part-fixture contacts are modelled as spring-dashpot elements. Piezoelectric actuators are utilized to provide the forces required for the adaptive clamping scheme. A model-based control architecture has been incorporated and proportional—integral (PI) controllers are established for the individual clamps. After investigating the performance of the controllers for dynamic compensation, analysis shows that PI control can be used effectively to minimize the reaction forces on the supports, induced by deflection caused by machining forces.

Fixturing and tooling for wing assembly with reconfigurable datum system pickup

The aerospace manufacturing sector is continuously seeking automation due to increased demand for the next generation single-isle aircraft. In order to reduce weight and fuel consumption aircraft manufacturers have increasingly started to use more composites as part of the structure. The manufacture and assembly of composites poses different constraints and challenges compared to the more traditional aircraft build consisting of metal components. In order to overcome these problems and to achieve the desired production rate existing manufacturing technologies have to be improved. New technologies and build concepts have to be developed in order to achieve the rate and ramp up of production and cost saving. This paper investigates how to achieve the rib hole key characteristic (KC) in a composite wing box assembly process. When the rib hole KC is out of tolerances, possibly, the KC can be achieved by imposing it by means of adjustable tooling and fixturing elements. A test rig has been designed and built that is used to experimentally investigate the capability of both the tooling and fixturing concepts. Some experiments have been carried out that successfully demonstrate the capability of the reconfigurable fixturing technology to achieve the rib hole KC.

Model-Based Control of an Advanced Actuated Part-Fixture System

In this paper the dynamical behavior of a part and an actuated fixture system is studied. The part is modeled using the finite element method. Subsequently, a reduced model is established using the Craig-Bampton reduction method in order to create a small-sized model, accurately describing the dynamic behavior of the part. The clampers and locators of the fixture are modeled as springs. The fixture frame is considered to be much stiffer than the locators such that it provides zero displacement boundary conditions to the locators. An electromechanical actuator is utilized to provide the adaptive clamping forces. After investigating proportional control, integral control, the three term classical PID controller and a lag filter for dynamic compensation, the analysis shows that position feedback can be used effectively in combination with integral control action to minimize unnecessary displacement of the workpiece and increase the bandwidth of the actuated fixture system.Copyright

Manufacturing Technology: Micro-machining

Micro-machining technologies have been the subject of many studies and developments over recent decades due to their importance in the production of micro-moulds, micro-valves, medical components, micro-electrical-mechanical-systems, sub-miniature actuators, motors and micro-products generally. This chapter defines some key terms (in the context of micro-machining) and then outlines material considerations, challenges in obtaining the desired surface finish, simulation techniques, process and machine aspects of micro-machining, and it finally provides examples of micro-manufacturing sectors and applications.

Recent research on flexible fixtures for manufacturing processes

Fixtures, are used to fixate, position and support workpieces, and form a crucial tool in manufacturing. Their performance influences the manufacturing (and assembly) process of a product. Furthermore, fixturing can form a significant portion of the needed investment and total process planning time for the manufacturing system. Many fixturing concepts, as contribution to increase the flexibility of the manufacturing system, are reported in the literature. The flexible fixturing designs can be classified into the following seven categories: modular fixtures, flexible pallet systems, sensor-based fixture design, phase-change based concepts, chuck-based concepts, pin-type array fixtures and automatically reconfigurable fixtures. It is observed that the more intelligent and automated fixturing systems are designed with the demands for automation in certain industries in mind. Furthermore, different fixturing solutions suit the engineering demands for different manufacturing areas, this means that for the foreseeable future all technologies will remain current. From the self-reconfigurable fixturing techniques a new fixturing capability is emerging: in process reconfigurability for the optimal placement of clamps and supports during the whole process time. These several concepts together with some recent patents are studied here. The paper concludes with some prospective research directions in the field of flexible fixturing.

Interfacing Belief-Desire-Intention Agent Systems with Geometric Reasoning for Robotics and Manufacturing

Unifying the symbolic and geometric representations and algorithms used in AI and robotics is an important challenge for both fields. We take a small step in this direction by presenting an interface between geometric reasoning and a popular class of agent systems, in a way that uses some of the agent’s available constructs and semantics. We then describe how certain kinds of information can be extracted from the geometric model of the world and used in agent reasoning. We motivate our concepts and algorithms within the context of a real-world production system.

Variation Aware Assembly Systems for Aircraft Wings

Aircraft manufacturers desire to increase production to keep up with anticipated demand. To achieve this, the aerospace industry requires a significant increase in the manufacturing and assembly performance to reach required output levels. This work therefore introduces the Variation Aware Assembly (VAA) concept and identifies its suitability for implementation into aircraft wing assembly processes. The VAA system concept focuses on achieving assemblies towards the nominal dimensions, as opposed to traditional tooling methods that aim to achieve assemblies anywhere within the tolerance band. It enables control of the variation found in Key Characteristics (KC) that will allow for an increase in the assembly quality and product performance. The concept consists of utilizing metrology data from sources both before and during the assembly process, to precisely position parts using motion controllers. In this way the assembly fastening operations can be performed optimally and account for manufacturing induced dimensional variations that reduce cycle times in aircraft wing assembly processes. By alleviating the dimensional variation caused by the upstream manufacturing processes and the inaccuracies in the tooling we will achieve a significant increase in the capability of aircraft wing assembly. To analyze the effectiveness of the VAA system a rib insertion process, occurring in a typical aircraft wing assembly, was replicated on a demonstrator test rig. Industrial grade motion controllers and metrology equipment ware utilized to allow for comparison to current industry practices. The experimental case study is described and initial process data shows promise for future implementation on a full scale assembly system.

Experimental Validation of Active Fixture Design Methodology

A design methodology for active and fully-active fixtures has been established previously. In this work the results of a part of the validation for the design are presented, namely the differences between two different layouts and the difference between application of an passive and active clamp. The test-bed consist of a reconfigurable fixturing system with an active clamp holding a thin-walled plate. For three cases passive and actively controlled clamping forces were exerted during a series of milling operations. These are (1) passive clamping at a suboptimal and (2) at the optimal position and (3) clamping with an actively controlled clamping force at the optimal clamping location. The previously proposed design procedure has been qualitatively validated since its predictions regarding optimal layout and adaptive clamping forces hold true, when comparing the surface finishes, which improve from case to case.Copyright