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In this paper, we focus on the development of a machine for manufacturing needle probes used in the electrical testing of printed circuit board (PCB) in-circuit-test fixtures. Currently, the manufacturing process for needle probes involves manual tasks such as wire threading, soldering, heat shrink tubing application, heat shrink tubing heating, and placing cylindrical terminals into a needle disc. Owing to the time-consuming nature of this production process, automation is proposed for improvement. The system development involves programmable logic controller (PLC) control and pneumatic cylinder mechanisms to replicate the manual wire threading process. Pneumatic grippers are used to position cylindrical terminals and heat shrink tubing. Two stepper motors drive plastic rollers for copper wire extension by a rolling process along V-shaped groove straightening guides, reaching the wire insertion holes on the PCB. A YZ-axis servo stage with clamping fixtures secures the PCB and moves it to the wire insertion holes. Once the copper wire extends through the cylindrical terminal, the threading action for that PCB hole is completed. Subsequently, laser welding joins the cylindrical terminal with the copper wire, and a hot air blower fuses the heat shrink tubing with the cylindrical terminal. Pneumatic grippers grasp the threaded cylindrical terminals. Simultaneously, an XY-axis servo stage with clamping fixtures places the disc into the clamping fixture, moves it beneath the pneumatic grippers, and inserts the cylindrical terminals into the disc. After completion, a few centimeters of copper wire in front of the rollers are cut, marking the completion of the needle placement for that hole on the disc. The combination of PCB hole wire threading and disc hole needle placement constitutes one cycle of the wire threading fixture. The machine repeats this automated sequence until the entire needle probe fixture is produced. [ABSTRACT FROM AUTHOR]

Composite structures in aeroplanes are often thin-walled and lightweight, resulting in significant compliance, which presents a handling and assembly challenge due to the associated part deformations. In order to counteract these deformations, the parts are held in their specified geometry using stiff and correspondingly heavy fixtures or jigs. Mobile industrial robots are very versatile and widely used in industrial volume production, but they are limited in their payload capacity. High-rate production of large aerospace modules requires highly automated flexible assembly processes. The approach presented in this paper is to combine mobile units with lightweight assembly jigs that have the capability of deformation compensation. The subject of the study is a high-rate assembly process for flap modules using an Autonomous Industrial Mobile Manipulator (AIMM) and a lightweight end effector. The end effector has a shape compensation function, implemented by an integrated Stewart platform, which enables the compensation of manufacturing tolerances as well as gravity effects. The compensation function is used in a closed loop and counteracts shape deviations by appropriate fixture shape adjustments. The paper reports on the conceptual design of the assembly scenario, the design of the end effector, its realization and the successful experimental demonstration at 1:1 scale. [ABSTRACT FROM AUTHOR]

As an important component of the machining system, the influence of fixtures on the machining deformation of the workpiece cannot be ignored. By controlling the clamping force during the machining process is an effective means to suppress or improve the machining deformation. However, due to the dynamic coupling of part geometry, clamping method, manufacturing process and time-varying cutting forces, it is difficult to obtain accurate clamping forces, which hinders the realization of fixture-based deformation control. In this paper, the variation of clamping force is considered as the response of the joint action of cutting force and other working conditions in spatial and temporal terms, and a clamping force prediction method based on deep spatio-temporal network is proposed. The part geometry model is first parameterized based on voxels, after which the cutting forces are dynamically correlated with the clamping forces in spatial and temporal terms. Then, a convolutional network was designed to capture the spatial correlation between the working conditions such as cutting force and clamping force, and a gated recurrent cell network to capture the temporal correlation to predict the clamping force during machining. Finally, an experiment of milling a cylindrical thin-walled part illustrates the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Measuring impedance accurately requires dedicated fixturing to match the geometry of the device under test to the ports of the instrument. These fixtures introduce error into collected measurements which is rarely acknowledged. Failure to quantify measurement error can lead to over-estimation of accuracy, increase the difficulty of measurement comparisons taken with different fixtures, and increase the risk of inappropriate fixture selection and calibration. This paper presents a methodology for characterizing and modeling the error introduced into impedance data by test fixtures. The proposed method uses direct measurements of the open- and short-calibration standards as well as a precision resistor to quantify the total error introduced by the fixture. The error of a commercially available test fixture is studied and compared with its published values to validate this method. This validated approach can model the error introduced by commercial or custom fixtures. [ABSTRACT FROM AUTHOR]

Modelling the dimensional variation propagation in multi-station machining processes (MMPs) has been studied intensively in the past decade to understand and reduce the variation of product quality characteristics. Among others, the Stream-of-Variation (SoV) model has been successfully applied in a variety of applications, such as fault diagnosis, process planning and process-oriented tolerancing. However, the current SoV model is limited to the MMPs where only fixtures with punctual locators are applied. Other types of fixtures, such as those based on locating surfaces, have not been investigated. In this paper, the derivation of the SoV model is extended to model the effect of fixture- and datum-induced variations when fixtures with locating surfaces are applied. Due to the hyperstatic nature of these fixtures, different workholding configurations can be adopted. This will increase the dimension of the SoV model exponentially and thus may make the model-based part quality prediction extremely complex. This paper presents a method of reducing the complexity of the SoV model when fixtures based on locating surfaces are applied and evaluates the worst-case approach of the resulting part quality. [ABSTRACT FROM AUTHOR]

A cylindrical structure used in a space launch vehicle should endure the compressive load and it must satisfy the requirement of compressive strength. For the light-weight of the structure and improving the performance of launch vehicle, a cylindrical structure reinforced by composite lattice can be used. Therefore, a compressive strength prediction technique of the cylindrical composite lattice structure is required. In this paper, the failure criterion was proposed using the compression test of a composite lattice subelement and a simple finite element analysis for the subelement. The failure criterion was introduced using the effect of the out-of-plane and in-plane bending deformation of the rib constituting the grid of structure on the compressive strength. The subelement specimen was prepared from two different structures and the compression test was performed using several fixture jigs which can generate various deformation of the specimen. The test results and finite element model were used to examine the effect of out-of-plane and in-plane bending deformation of the rib on the compressive strength and the failure criterion which can predict the compressive strength was derived using the relationships between each parameter. The compressive failure load of the cylindrical composite lattice structure was predicted by using the proposed method and the validity and accuracy of this method were verified through a comparison of the predicted results with the test results. It was possible to predict the compressive strength within a 5% error of the experimental result. [ABSTRACT FROM AUTHOR]

An alternative method to reduce setup time is to simultaneously carry out fixture planning for several parts in one setup planning. This is possible due to the size of parts which are relatively small to the size of the machine work bed, typically found in a make-to-order industry. This research proposed a fixture planning method for multi-workpiece setup. The fixture planning method comprised two stages: 1) multi-workpiece layout and 2) 3-2-1 pin location. An example of multiple workpiece setup is illustrated in this paper to point out the method's applicability. Future research activity will integrate the proposed collaborative human-robot assembly design system method. [ABSTRACT FROM AUTHOR]

This paper presents a work undertaken in a pipe line manufacturing company which welds (butt joints) different diameter of pipes which are used for manufacturing of boiler. In order to weld two separate pipes, initially both of them has to be aligned and dimensionally checked to reproduce the data in the Engineering drawing. It takes up a lots of time and man power. And also, to make sure that the pipes do not lose its orientation, after the aligning bridge pieces are tag welded with the pipes to arrest all the degrees of freedom of the pipes and thereby immobilizing it. Our project gives the alternative for welding of bridge pieces in pipes for butt joints. By implementing the suggestion of carrying out the process by using fixture, we can reduce the total welding and fit-up time to 75% of the actual time. It also neglect other major problems such as, welding of brittle materials like P91, unnecessary reworks, human efforts, reduction of defects on parent material. [ABSTRACT FROM AUTHOR]

Fixtures are used for orientation-positioning-tightening of workpieces during machining on machine tools. Multiple clamping fixtures are intended to clamp several workpieces for simultaneous or successive machining. Multiple clamping is characterized by a series of economical advantages, due to the reduction of total machining time. These advantages are more important once the number of workpieces is higher or if the machining is made with compound tools. Due to the complexity, overall size and the high number of components, the multiple clamping fixtures have diminished accuracy than simple fixture due to elastic and contact deformations of fixtures housing, of supports etc. Also, multiple clamping fixtures present diminished rigidity and dynamic stability. From the analysis of the specialized literature results that there are a few paper on the subject of multiple clamping. In the paper there are presented the causes that can lead to the diminishing of the accuracy of multiple fixture. The modalities for the determination of fixtures precision are presented, also, for the parallel and serial multiple clamping fixtures. [ABSTRACT FROM AUTHOR]

The manufacturing of composite parts and assemblies requires various kinds of tools, which determine the accuracy, performance, and cost of the end component. Additive manufacturing (AM), also known as 3D printing technology, has a direct impact on the manufacturing the of composite structures by offering rapid production of molds. 3D printing of molds, jigs and fixtures for composites manufacturing increases flexibility and design opportunities and reduces costs and lead time. Large-format AM systems, that can create an object larger than 1 m3, are the only systems that are suitable for rapid production of molds. Most of these systems are based on single-screw thermoplastic pellet extruders. Massivit 3D has developed a unique technology called Cast-In-Motion (CIM) and a designated system, the Massivit 10000, for direct digital printing of tools and molds, made of a proprietary epoxy-based, Thermoset casting material, CIM 500. The technology consists of printing a double-wall shell made of a proprietary UVcured Water Breakable (WB) material, Dimengel 50, followed by casting a calculated amount of CIM 500. The WB printing process and the thermoset-casting processes operate intermittently to create a near net shape, thermoset mold encapsulated by the WB shell. After the encapsulated mold is cured to optimize its mechanical properties at elevated temperatures, it is immersed in a water bath which causes the shell to crumble away and can be post finished to obtain the desired surface finish and geometry for the mold. The system can also be used for the printing of geometric cores and soluble mandrels for the composites industry by utilizing the printing of the WB and other various acrylic base UV cured materials without the conjunction of the CIM 500. This paper presents the advancements in CIM technology with its proprietary materials to enable direct manufacturing of complex finished molds. It also presents various applications from the design phase through printing to post finishing that meet customers' requirements. [ABSTRACT FROM AUTHOR]

The elastic deformation of thin-walled workpieces is because of the combination effect of cutting force and clamping force, which also leads to processing error. Clamping force and cutting force have coupling effect during this process. Clamping force and cutting force are mainly influenced by fixture, and cutting parameters, respectively. Instead of considering coupling effect of clamping force and cutting force when optimizing fixture and cutting parameters step by step, this paper establishes a recursive optimizing model through particle swarm optimization (PSO) and finite element (FE) methods to optimize fixture and cutting parameters simultaneously. With the guidance of PSO under certain deformation conditions, FE analysis finds optimal combinations of fixture and cutting parameters, which reduce elastic deformation of thin-walled workpieces. The case study shows that the model had achieved optimization results. It effectively reduced elastic deformation of thin-walled workpieces during processing and improved the machining accuracy. [ABSTRACT FROM AUTHOR]

Fixture errors are one of the error sources in machining operations. The fixture errors consist of positioning inaccuracies and errors due to workpiece and fixture deformations. Fixture locators’ height error causes incorrect positioning of the workpiece in the fixture and inaccuracy in machined surfaces which can be much more than the locators’ height error. For machining precise workpieces, it is necessary to eliminate these errors. This paper presents a method for modelling and compensating the fixture locators’ height error effect on workpiece machined surfaces. In this method, the planes of workpiece actual coordinate system (ACS) are mathematically modelled in the workpiece theoretical coordinate system (TCS). Using the model, required homogenous transformation matrix for coinciding ACS with TCS and modifying machining toolpath for compensating the errors is generated. The presented model is used to develop a post-processing fixture locator error compensation module, which can modify CNC machining codes to eliminate the effect of fixture locators’ height error on the workpiece machined surfaces. For verifying the presented method, machining simulations and cutting experiments have been performed in this work. The results show that the method can eliminate the effect of fixture locators’ height error on the workpiece machined surfaces considerably. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

In the design of a machining fixture configuration (layout), the stability of the fixture, which influences the dimensional and form accuracy of the workpiece, is an important factor. The optimal placement of the fixturing elements minimizes the dynamic response of the workpiece (elastic deformation of the workpiece under dynamic conditions), which in turn improves the stability of the fixture. In this paper, an Ant Colony Algorithm (ACA) and Genetic Algorithm (GA) are employed to optimize the fixture layout with an objective of minimizing the dynamic response of the workpiece. The different node systems are used on the same workpiece geometry, and the fixture layout is optimized so that the elastic deformation of the workpiece satisfies the accuracy needed on the workpiece. Two different examples are used to compare the performance of ACA- and GA-based fixture-layout optimization methods. [ABSTRACT FROM AUTHOR]

In recent years, the growing need for reducing non-structural damage after earthquakes has stimulated a dedicated effort to develop innovative types of fasteners for anchoring non-structural components (NSCs) to reinforced concrete (RC) host-structures. To contribute to such need, and building on previous research, this paper presents the results of a series of uni-directional shake-table tests of simulated NSCs anchored to concrete via: (1) expansion, and (2) chemical anchors; post-installed into: (a) uncracked, and (b) cracked concrete. Considering different construction details, the experimental investigation focused on traditional anchorage systems, alternative solutions comprising mortar filling into the gap clearance, and a low-damage system relying on supplemental damping devices, capable of reducing the acceleration of the NSCs as well as the force of the anchorage during seismic shakings. The experimental tests provided significant evidence on the beneficial effects of a dissipative anchorage protecting both the non-structural component and the anchorage itself, even during strong earthquakes. Moreover, when construction details allow to close the fixture clearance with a mortar filling, this stiffer solution provide an additional reduction of NSCs seismic accelerations and forces. Therefore, suggestions for further improvements of the adopted low-damage solution are also proposed. [ABSTRACT FROM AUTHOR]

This paper considers the effect of natural material compliance on the stiffness and stability of frictional multi-contact grasps and fixtures. The contact preload profile is a key parameter in the nonlinear compliance laws governing such contacts. The paper introduces the Hertz–Walton contact compliance model which is valid for linear contact loading profiles. The model is specified in a lumped parameter form suitable for on-line grasping applications, and is entirely determined by the contact friction and by the material and geometric properties of the contacting bodies. The model predicts an asymmetric stiffening of the tangential reaction force as the normal load at the contact increases. As a result, the composite stiffness matrix of multi-contact grasps governed by natural compliance effects is asymmetric, indicating that these contact arrangements are not governed by any potential energy function. Based on the compliant grasp dynamics, the paper derives rules indicating which contact point locations and what preload profiles guarantee grasp and fixture stability. The paper also describes preliminary experiments supporting the contact model predictions. [ABSTRACT FROM PUBLISHER]

Some recent studies have addressed a class of human-machine coordination employing "virtual fixtures," which are computer-generated walls or guides presented through haptic devices for assisting precise path tracing and for preventing the entry to specified regions. This paper presents the concept and control algorithms of a new class of virtual fixtures that is based on simulated plasticity. The plasticity-based virtual fixtures act as hard walls as long as the user's force is smaller than a predetermined yield force, but the user can deviate from the fixtures by intentionally producing a force larger than the yield force. As a characteristic of plasticity, the proposed virtual fixtures do not store elastic energy; the reaction force from the fixture almost always opposes the user's motion to decelerate the motion. Thus, the plasticity-based virtual fixtures are expected to be useful in some applications where safety is an utmost priority. This paper presents control algorithms for realizing the concept of plasticity-based virtual fixtures, addressing technical challenges in treating discontinuous nature of plasticity in discrete-time systems. The algorithms were demonstrated through experiments using impedance-type and admittance-type haptic devices. [ABSTRACT FROM AUTHOR]

The tolerances of a part influence both the operation of the assembly of which it is part and the technological manufacturing process. High tolerances can lead to an assembly that does not work at the designed parameters, and low tolerances require additional machining operations that increase the cost of the part. The manufacturing series is another factor that influences the technological process. Large series production requires special facilities in terms of processing and control equipment which are needed in the manufacturing process. The paper presents a case study on the influence of tolerances of a part being produced in large series on the construction of the orientation and clamping device used in machining. Starting from the dimensions indicated in the design drawing, a first version of the fixture is proposed in which the parts are fixed and the tolerance of the closing dimension of the assembly of parts is analysed using the Worst Case and Root-Sum-Square methods. Since the closure size tolerance is outside the recommended range, another variant of orientation and fixture is proposed. By re-analysing, the closing dimension tolerance by the two methods mentioned above it was confirmed the necessity of modifying the part width tolerance. The analysis of the tolerance of the closing quota is resumed by the two methods mentioned above and the result confirms that it is necessary to change the tolerance to the width of the piece. The tolerance verification of the closure dimension of the assembly formed by the parts fixed in the device is performed by Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Conventional design of jigs and fixtures has become unsuitable given the requirements of modern technology and complexity and diversity in the production with the rapid update of products. Computer-aided design (CAD) of jigs and fixtures is an effective solution in this direction. The current paper focuses on a computer-aided design of the traditional jigs and fixtures and developed a system containing tailor-made software, created using the Visual Basic programming language and installed on it the viewer screen to show the part. The developed system has been built by connecting Visual Basic programming language to the SolidWorks software on which the part is drawn and saved as STEP AP-203 file format, and the system reads and extracts the data from the STEP AP-203 file. Heuristic rules of feature recognition are pre-prepared for checking the extracted geometric data and deciding which data shape will represent the machining feature; then, the system provides the optimum design of the traditional jigs and fixtures for a group of hollow cylindrical parts that contain a group of cross-holes on the cylinder body, whether perpendicular or offset from the cylinder's axis, (inclined or inclined offset, or blind or through, by applying pre-prepared heuristic rules for the design of traditional jigs and fixtures. [ABSTRACT FROM AUTHOR]

A Computer Aided Fixturing System (CAPS) was used in this paper to study the planning of modular fixtures for measurement using a Coordinate Measuring Machine (CMM). This paper proposes fixturing planning of a complicated small supporting face and a large general supporting face. Group Technology (GT) was used to establish the coding database of the modular fixture element for use in the system. Several algorithms are developed to locate the appropriate fixture elements and their positions. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to develop a special modular fixture system for machining and drilling parts that hold pneumatic jacks componets. This family of parts is usually made in various dimensions and sizes but with a specific geometric shape. The design requirements of the restrictions, the way of the construction process is considered as the design inputs of this system. Positioning and clamping system have been designed, modeled and simulated for the mass production of a family of these parts with minimal changes in the manufacturing process. The results obtained from the idea of designing such restraints in machining processes show that with its help, it is possible to reduce the design and manufacturing costs of restraints for a group of parts that are similar in appearance but different in size and dimensions. It will significantly reduce and minimize the time of adjusting these equipments during the production process and will increase the productivity and circulation of products. [ABSTRACT FROM AUTHOR]

Background : Tapping is one of the processes that most requires attention in the industry, due to the stage in which it occurs and its characteristics. In the case of tapping, it is common to use components and equipment with less rigidity, which compromises the dynamic behavior in several situations and can lead to process distortion or failure. Purpose: The objective of this paper is to study the dynamic behavior of tapping in relation to several characteristics of the process. Methods : The dynamic behavior of the force signal was used to evaluate the process, varying the cutting parameters and the clamping system of the workpiece. Results: The experimental results indicate that the floating system did not present a good dynamic behavior at high cutting speeds, this greater application of vibration is due to the resonance due to the combination of oscillations under forced and natural vibration. Conclusions: The natural frequency of the floating fixture system influenced the behavior of the axial forces. The increase in cutting speed resulted in a direct increase in the axial force vibrations as its frequency came close to the natural frequency of the system. Through dynamic analysis of the axial force signal observed the dynamic characteristics of the process and the machine tool. This allowed the dynamic evaluation of the system through the measurement of force signals generated in the threading process. [ABSTRACT FROM AUTHOR]

Among the chatter suppression techniques in milling, active fixtures seem to be the most industrially oriented, mainly because these devices could be directly retrofittable to a variety of machine tools. The actual performances strongly depend on fixture design and the control logic employed. The usual approach in the literature, derived from general active vibration control applications, is based on the employment of adaptive closed-loop controls aimed at mitigating the amplitude of chatter frequencies with targeted counteracting vibrations. Whilst this approach has proven its effectiveness, a general application would demand a wide actuation bandwidth that is practically impeded by inertial forces and actuator-related issues. This paper presents the study of the performance of alternative open-loop actuation strategies in suppressing chatter phenomena, aiming at limiting the required actuation bandwidth. A dedicated time-domain simulation model, integrating fixture dynamics and the features of piezoelectric actuators, is developed and experimentally validated in order to be used as a testing environment to assess the effectiveness of the proposed actuation strategies. An extensive numerical investigation is then carried out to highlight the most influential factors in assessing the capability of suppressing chatter vibrations. The results clearly demonstrated that the regenerative effect could be effectively disrupted by actuation frequencies close to half the tooth-pass frequency, as long as adequate displacement is provided by the actuators. This could sensibly increase the critical axial depth of cut and hence improve the achievable material removal rate, as discussed in the paper. [ABSTRACT FROM AUTHOR]

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The comanipulation paradigm, in which a user and a robot simultaneously hold a tool, allows for gesture guidance. In particular, virtual fixtures, which are geometrical constraints imposed to the tool by the robot, have received great interest in the domain of surgical applications. So far, this concept has been implemented in the context of open surgery. This paper explores the application of virtual fixtures for minimally invasive surgery, in which the tool is inserted in the patient through a fulcrum. Here, a key issue is to return to the surgeon forces that are virtually applied at the instrument distal tip, while the robot is physically attached to the instrument proximal handle. To this aim, two approaches are investigated. A first approach consists of applying a full wrench at the proximal end of the instrument that is equal to the wrench constituted by a pure force applied to the instrument's distal tip. A second approach consists of applying a pure force to the instrument proximal end, thanks to a lever model about the fulcrum. The two approaches are compared through experiments, during which naive subjects blindly perform virtual object palpation and robot-guided movements. During experiments, indicators involving motion and force analysis are computed. The user capacity to distinguish between several virtual objects is evaluated as well. Although drastically different, the two approaches provide assistance with a similar level of efficiency. [ABSTRACT FROM AUTHOR]

The fixture determines the workpiece position in a machining process; therefore, an increasing amount of attention has been given to fixture layout design. While machining, the workpiece position is affected by two major sources: (a) the locator displacement and (b) the force-deformation of the workpiece-fixture system. In the beginning of this paper, a geometric model considering the shape of a locator is developed to analyze the location performance, followed by the presentation of a simplified solving method and a location layout performance index. Second, to complete the force-deformation analysis, a finite element method-based force-deformation model is built and accelerated by a new method with a lower computer memory cost. Based on these two models, multiple objects of fixture layout optimization problems are proposed, and a multi-objective genetic algorithm-based optimization method is constructed. Finally, testing examples are approved to examine the validity of the method represented in this paper. These methods can provide a more accurate prediction of the locating performance in more widely used cases, and they have faster calculating speeds with lower computer memory costs. [ABSTRACT FROM AUTHOR]

Radio Frequency Identification (RFID) technology presents automatic identification technology that can be used in product life cycle various phases, especially in the manufacturing phase. The analysis of possible application of RFID technology in machining and inspection operations for fixture manufacturing assembly/disassembly process is presented in this paper. Furthermore, assemble/disassemble fixture manufacturing system structure and conception is presented. An analysis involves hardware and software components that the designed system for assembly/disassembly needs to have. Suggested system verification was done in laboratory conditions. Verification uses ninety-six parts and adequate fixtures. The paper concludes with final remarks, discussing advantages and disadvantages of the developed system. [ABSTRACT FROM AUTHOR]

Purpose - Fixture failures are the main cause of the dimensional variation in the assembly process. The purpose of this paper is to focus on the optimal sensor placement of compliant sheet metal parts for the fixture fault diagnosis. Design/methodology/approach - Based on the initial sensor locations and measurement data in launch time of the assembly process, the Bayesian network approach for fixture fault diagnosis is proposed to construct the diagnostic model. Furthermore, given the desired number of sensors, the diagnostic ability of the sensor set is evaluated based on the mutual information of the nodes. Thereby, a new sensor placement method is put forward and validated with a real automotive sheet metal part. Findings - The new proposed method can be used to perform the fixture fault diagnosis and sensor placement optimization effectively, especially in a data-rich environment. And it is robust in the presence of measurement noise. Originality/value - This paper presents a novel approach for fixture fault diagnosis and optimal sensor placement in the assembly process. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to present a novel approach for identification of machining fixtures, and their elements in an assembly/disassembly process. Design/methodology/approach - Radio frequency identification (RFID) technology is applied to identification of physical machining fixtures and their basic elements. Findings - Based on comprehensive testing in industrial conditions it was established by this research that the use of RFID technology contributes to significant reduction of assembly/disassembly time of machining fixtures. Practical implications - Practical applicability of RFID technology is emphasized and demonstrated in the paper. The suggested system is proven superior in comparison with conventional methods for identification of fixtures/fixture elements which qualifies it for real industrial application. Originality/value - To the best of authors' knowledge there are no previous reports of successful application of RFID technology on identification of fixtures/fixture elements. [ABSTRACT FROM AUTHOR]

The article presents information on a research paper which proposes an optimal method for sensor placement for the fixture variation diagnosis of compliant sheet metal assembly process. It is said that fixture variations are one of the most common reasons for complex automotive body dimensional failures. It is said that an effective measurement strategy is required to diagnose these variations. The paper analyzes the relationship between the assembly variation and fixture variations with the help of the method of influence coefficients. It uses effective independence (EI) method to find the optimal sensor positions.

A key process in assembly of microelectromechanical systems optical switches is of inserting fibers into U-grooves in silicon substrate. Due to positioning errors and dimensional tolerances in components, heavy collision occurs between fibers and the edges of U-grooves during insertion, throwing out fibers from the fiber holder or worse, damaging the components. Typical solutions to the problem involve determining errors using machine vision or force sensors, and then positioning fibers accurately by virtue of high precision multi-axis systems (with submicron repeatability). However, these approaches are costly and difficult to implement. In this paper, we present a low-cost passive assembly method to solve the problem. It utilizes a special flexure-based fixture to regulate high contact forces and accommodate assembly errors. Specifically, we model the problems happening in the process of fiber insertion and characterize the conditions of successful insertion. We then suggest how to design flexural fixtures so that the required insertion conditions can be met. Experimental results show that using such a fixture the fiber assembly can be successfully implemented even if the assembly system's accuracy is lower than 12 µm in x and y axes, and 0.07° in theta axis. These requirements are within the reach of most low-cost precision systems. Note to Practitioners—In the assembly of optical switches, heavy collision occurs during inserting fiber into U-grooves due to positioning errors and dimensional tolerances in components. It may result in fiber skidding out from the gripper, or the component damage. This paper aims to present a low-cost but effective method to solve the problem. The idea is utilizing a special "floating" fixture that can self-regulate high contact forces and accommodate assembly errors. This fixture is designed with flexures. In practical application, it can be built either as a standalone component or as an embedded mechanism built-in on the chip. Preliminary physical experiments show by adopting such a fixture, fibers can be inserted into U-grooves without any skidding and damage even if using normal pick-and-place systems. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the optimal design of fixture layouts in multistation assembly processes. An optimal fixture layout Improves the robustness of a fixture system against environmental noises, reduces product variability, and leads to manufacturing cost reduction. Three key aspects of the multistatlon fixture layout design are addressed: a multistation variation propagation model, a quantitative measure of fixture design, and an effective and efficient optimization algorithm. One of the challenges raised by this multistation design is that a high-dimension design space, which usually embeds a lot of local optimums, will have to be explored. Consequently, it makes a global optimality more difficult and, if an inefficient algorithm is used, may require prohibitive computing lime. In this paper, exchange algorithms, originally developed in the research of optimal experimental design, are adopted and further revised to optimize fixture layouts in a multistation process. The revised exchange algorithm provides a good tradeoff between optimality and efficiency: it remarkably reduces the computing time without sacrificing the optimal value. A four-station assembly process for a sports utility vehicle sideframe is used throughout the paper to illustrate the relevant concepts and the resulting methodology. [ABSTRACT FROM AUTHOR]

Fixture design plays an important role at the planning stage before shop-floor production. A desired fixture design can be employed to hold the workpart securely so that slippage and excessive deformation can be prevented during machining. Therefore, appropriate fixturing contributes highly to machining quality. To reduce lead time and the human effort devoted to fixture planning, computer-aided fixture design (CAFD) is required. In this paper, a CAFD system consisting of three modules, i.e. Fixture Data Management, Fixture Element Selection and Fixture Layout Design, is developed. According to fixture feature recognition and classification, a comprehensive fixture database in the Fixture Data Management module is constructed to maintain efficiently the fixture-related data. The domain of the fixture database consists of modular mechanical fixtures, modular hydraulic fixtures and modular V-blocks. After expertise extraction, suitable fixture elements can be automatically selected according to the machining conditions in the Fixture Element Selection module. Finally, by integrating previous reasoning algorithms, fixturing locations and orientations are determined. Feasible fixture layouts that meet manufacturing and inspection specifications can be generated in the Fixture Layout Design module. The prototype system is implemented under commercial CAD and database management system (DBMS) software. Comprehensive fixture databases and a rule-based knowledge base are built to provide effective data management. The paper aims to propose a systematic CAFD framework and application system to provide efficient decision support for different types of fixture planning. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm to compute the globally optimal fixture with frictionless contacts in a discrete point set on an object. The capability of a fixture to immobilize the object is evaluated by the minimum of the largest conflict of the object with the contacts over all motion directions, which can be reduced to the radius of the largest origin-centered ball contained in the convex hull of primitive contacts wrenches. All candidate fixtures (combinations of the discrete points of a certain number) are expressed in a tree structure, in which each node contains a discrete point representing a contact location and each path from the roots to a leaf represents a fixture. A preorder walk of the tree is performed to search for the optimal fixture. Necessary conditions are derived to predict whether the subtree of a node contains a better fixture. If any necessary condition is not met, then all the fixtures contained in the subtree can be simply rejected. By this means only a small portion of the tree will be traversed and the globally optimal fixture can be found more quickly. This algorithm has been tested on various three-dimensional objects and has been found to be over ten times faster than the brute-force search. [ABSTRACT FROM PUBLISHER]

Proposed in this paper is a novel approach to fixture layout design. The contact interface between workpiece and fixture is reduced to a single workpiece surface. This allows reliable machining of the remaining five workpiece surfaces in a single setup. Workpiece clamping is performed by inserting special elements into prepared auxiliary openings on the workpiece. Clamping is thus reduced to indenting of sharp clamping element tips into the workpiece surface. Shallow indenting is performed on surfaces which have no practical function. Special device was designed to allow experimental investigation. Experimental results point towards the efficiency of the proposed approach. Workpiece displacements were small during machining and allowed the required machining accuracy. Furthermore, the results obtained during machining indicate high surface quality. [ABSTRACT FROM AUTHOR]

This paper presents a fixture generation methodology that takes into account dynamic machining conditions which occur when the machining forces and moments travel or change with respect to time. This is more realistic than previous systems which have treated the machining conditions as static. It also increases the difficulty of fixture generation since the machining conditions are always changing. In this paper, a comprehensive methodology based on linear programming has been developed to circumvent this problem. It takes into account the maximum forces and moments during all time and the desirable characteristics of a fixture such as: positive reaction forces at the locators for all time, deterministic positioning, strong accessibility, stability of the workpart in the fixture while under no external forces, and a positive clamping sequence. In order to reduce the total computation time, the linear programming technique is used to formulate the deterministic positioning and accessibility characteristics of a fixture. Finally, force planes, similar to distributed load diagrams, are created to act as guides in the slight repositioning of locators for modular fixturing. Two case studies are presented to demonstrate the capabilities of the methodology. [ABSTRACT FROM AUTHOR]

The two-axis gimbaled antenna’s performance can be greatly improved if it is statically balanced. This paper intends to present a novel design of a measurement system for use in statically balancing a two-axis gimbaled antenna mounted on an aircraft. The details of the measurement system and its working principle are explained, including the dynamics of the two-degree-of-freedom flexure-hinge leverage and the control configuration of the measurement system. The measurement principle is proposed after the theoretical measurement uncertainties estimated and the key factors that determine the measurement accuracy are found. By controlling the uncertainty induced from the major factors, the measurement accuracy can be finally controlled. The measurement result is proved sufficiently accurate by means of High-speed centrifuge method. [ABSTRACT FROM PUBLISHER]

Construction of the quality tolerances (Q-T) function is a key step in assembly tolerance analysis process. This paper presents a new feature-based tolerance analysis method for mechanical assemblies with GD&T, location tolerances, and fixture tolerances. In this method, tolerances and deviations are modeled by the small displacement torsor theory, the accumulation and propagation of deviations are expressed by the deviation propagation theory, and the quality requirements are solved by the deviations of specific features. Thus, the Q-T function relies on three sub-functions: tolerance deviation function, feature deviation function, and quality description function. Based on the functions, the paper presents an integrated solution for tolerance analysis. This method is competitive in three aspects: (1) the descriptions of the tolerances are close to reality, nonlinear relationships, and correlated tolerances can be analyzed as well; (2) the analysis process and acquired Q-T function is relatively concise to the other feature-based method; (3) the integrated assembly information is more intact. A case study is provided to illustrate the proposed method. [ABSTRACT FROM AUTHOR]

A review of the recent development of the machining fixture configuration/layout is presented in this paper. The literature review is mainly focused on the recently developed optimal fixture configuration under the dynamic conditions of the workpiece. In this review paper, the fixture design, fixture analysis, fixture synthesis, fixture layout design, optimization of fixture layout design, various optimization algorithms, and case studies of two- and three-dimensional workpiece geometries under dynamic conditions have been emphasized specially. The further scopes of the research are finally summarized. [ABSTRACT FROM AUTHOR]

The paper deals with some questions regarding workpiece clamping in fixtures from the point of view of production inaccuracies. These inaccuracies consist of deviation of medium economical accuracy, deviation of seating and deviation of the fixture. The final achievable workpiece accuracy depends on the components of the mentioned deviations. The paper describes influence of the support point choice on deviation extend of the surface machined. Way for workpiece seating deviation calculation is given in the paper when the workpiece seats on various supporting points. [ABSTRACT FROM AUTHOR]

This paper presents the results of 3‐point bending tests on 69 prenotched steel fiber reinforced concrete (SFRC) prisms conducted in accordance with EN 14651 to obtain the stress versus crack‐mouth‐opening displacement curves. SFRC prisms with fiber content greater than 20 kg/m3 and containing multiple hooked‐end fibers were found to exhibit deflection hardening behavior in bending after first crack. Based on the test results, empirical models to determine the residual flexural stresses are established through multiple regression analysis and further validated with test results available in the literature. The residual flexural strengths were found to be proportional to the reinforcing index, the square root of concrete compressive strength, and the square of the number of hooks at the fiber ends. Size effect is accounted for by introducing a factor which is a function of the fiber length. The empirical equations for the residual flexural strengths enable the use of Model Code 2010 constitutive relation for SFRC in tension without resorting to prism tests. [ABSTRACT FROM AUTHOR]

Wrong or inadequate design and manufacture of modular fixtures can lead to deformations and displacements of workpiece and fixture-workpiece assembly, as well. Deformations and displacements can significantly impact final workpiece accuracy, rendering the fixture less efficient. With that in mind, this paper reviews development of a novel multi-purpose solution for a modular fixture design with higher efficiency, higher accessibility and flexibility. The results of simulations and modelling indicate that the proposed modular fixture design has advantages over the existing, conventional modular fixtures. The proposed framed structure of modular fixtures exhibits versatility in that it allows reliable locating and clamping of workpieces featuring complex geometry and shape. The novel design solution for modular fixtures opens new directions for future investigation, regarding selection and optimization of materials, shape and geometry of fixture elements which can be used to extend and upgrade modular fixtures. All this contributes to higher workpiece quality and accuracy, as well as the higher productivity and lower production costs. [ABSTRACT FROM AUTHOR]

Object grasping and manipulation in robotics has been largely approached using visual feedback. Human studies on the other hand have demonstrated the importance of tactile and force feedback to guide the interaction between the fingers and the objects. Inspired by these observations, we propose an approach that consists in guiding a robot's actions mainly by tactile feedback, with remote sensing such as vision, used only as a complement. Directly sensing the interaction forces between the object, the environment, and the robot's hand enables it to obtain information relevant to the task that can be used to perform it more reliably. This approach (that we call sensitive manipulation) requires important changes in the hardware and in the way the robot is programmed. At the hardware level, we exploit compliant actuators and novel sensors that allow to safely interact and detect the environment. We developed strategies to perform manipulation tasks that take advantage of these new sensing and actuation capabilities. In this paper, we demonstrate that using these strategies the humanoid robot Obrero can safely find, reach and grab unknown objects that are neither held in place by a fixture nor placed in a specific orientation. The robot can also make insertions by \feeling" the hole without specialized mechanisms such as a remote center of compliance (RCC). [ABSTRACT FROM AUTHOR]

In the conditions of the increase in the range of products in the automobile and aircraft industry, there is a tendency to increase the scope of application of flexible fixtures. Thus, in the current article, it was proposed to consider a new concept of a flexible fixture for location parts of a complex shape. The stress and deflection of the steering knuckle elements were calculated using finite element modeling. During the experiment on the static loading, the deflection of the steering knuckle elements was measured, and the results of finite element modeling were validated. It was determined that the stiffness of the proposed flexible fixture ensures compliance with the tolerances of the mutual location of the surfaces of the part, making it reasonable for feature research the novel flexible fixture design during milling. [ABSTRACT FROM AUTHOR]

This paper presents a constraint-based approach to tolerance analysis in a multi-operation single setup and multi-operation multi-setup part–fixture assembly. First, several error sources are identified, modeled individually, and combined into a single accumulated error model that contribute to the final accumulated tolerances. This is used to determine the position and orientation of a machined feature. Second, the accumulated errors are expressed a function of the deviation parameters of the small displacement torsor (SDT). Third, a relationship is established between the tolerance requirements and the SDT parameters using a constraint-based mapping. The constraints capture the essential property of the part accuracy requirements and serve as boundaries for the machined feature. The method has the following advantages: (a) it establishes a direct link between error sources and part accuracy requirements, (b) it provides a direct way of evaluating the effect of each error source as well as their combined effect on part accuracy, and (c) it serves as a feedback system with the capability of providing advanced knowledge of the various physical behaviors of the part-to-fixture elements. Two simple examples are used to illustrate the approach. [ABSTRACT FROM AUTHOR]

Modern manufacturing engineering can hardly do without mandrels. In precision machining, turning, grinding, toothcutting and inspection, expanding mandrels are used for works with high requirements. The many different applications mean that there must be many different types ranging from hand-operated or power-assisted models through Morse taper or flange seat types, to various clamping ranges and various sundry special features such as self-locking clamps or workpiece stops with or without air sensing. This paper develops a novel analytical model for expanding mandrels. This paper first presents the analytical model to describe the operating principle of the expanding mandrels and the characteristics of the clamping/unclamping operation. Second, it presents the finite element method (FEM) analyses that were conducted to check the developed analytical model. The basic problem with the application of jaw-chucks for clamping workpieces during high-speed turning is the huge centrifugal force that acts on jaws. This centrifugal force reduces effectiveness of the clamping force, making the HSC process dangerous. With the application of expanding mandrels centrifugal force has not negative influence. [ABSTRACT FROM AUTHOR]

This paper deals with mechanical systems with passive contact elements, such as whole-hand grasps and fixture systems. The force closure problem in fixtures and manipulation systems with hybrid (active and passive) contacts is shown to be quite different from the pure active force closure in a multi-fingered robot hand. We discuss the conditions of active and passive force closure problems in such devices based on a rigid-body model with frictional contact. The contact force space is decomposed into three orthogonal subspaces: the space of external forces, the space of active internal forces, and the space of passive internal forces. The space of active internal force and the space of passive internal force play important roles in achieving the closure grasping. This paper presents an algorithm for computing the basis of each subspace. Based on this force decomposition, the force closure problem is formulated as linear matrix inequality feasibility problems, and minimization of the joint torque is also studied. [ABSTRACT FROM AUTHOR]

The parallel manipulators are used for many industrial applications in the aided manufacturing, thanks to their better performances: high precision and rigidity, high load capacity and high ratio between payload and net weight. One of the main goals of using parallel manipulators is to obtain better performance with respect to serial ones. On the other hand, the parallel manipulators suffer of some drawbacks. A very important one is the presence of singularities inside the workspace. It is very well known that the positioning accuracy of the platform of a parallel manipulator decrease with approaching to the singular position. One of the aims of the optimum design of the parallel manipulators is to obtain better performance, regarding the positioning precision of the platform and implicit -- of the end-effector, and the decrease of the driving forces. The present paper discuses in detail some aspects of the optimization problem of the parallel manipulator design, so that the positioning accuracy to be maximum. [ABSTRACT FROM AUTHOR]

In this paper we consider grasps and fixtures whose contacts react according to force—displacement laws consistent with friction constraints at the contacts. The passive force closure set of such grasps and fixtures is the set of external wrenches (forces and torques) that can act on the grasped object and be stably balanced by the contacts. An external wrench belongs to this set if it induces a feasible equilibrium whose basin of attraction contains the initial unperturbed grasp configuration. The paper focuses on planar grasps and fixtures having sharp-tipped fingers or fixels that satisfy linear force displacement laws. Using Morse theory, we characterize the number and stability type of k-contact equilibria induced by a given external wrench. Based on this analysis, we provide closed-form expressions for the passive force closure set of k-contact grasps and fixtures. Computation of the allowed external wrenches is illustrated with examples. Finally, the paper describes experiments verifying the passive force closure set on a spring-loaded grasping system. [ABSTRACT FROM AUTHOR]

Modern aerospace structures tend to consist of large numbers of geometrically complex structural components which by their very nature tend to suffer from significant levels of physical distortion and are thus difficult to assemble. One solution to this problem is to use large complex jigs which physically control the shape of the parts. These jigs are usually loaded using either direct manual labour or manual labour assisted by cranes or lifting devices. The use of manual operations represents a significant health and safety risk and increased likelihood of damaging components during assembly. The application of automation in the processing of such structures has so far been confined to small product specific cells owing to difficulties in pre-defining and fixing the exact geometry and positioning of parts within the work volume. The use of specially designed jigs, fixtures and aids such as drilling templates can be adapted to support automation but are expensive, have long manufacturing lead times and cannot be economically modified for use on other aircraft types. The paper proposes a solution to the above problems using standard industrial robots and an advanced control and non-contact metrology systems. The developed methodology is generic and has been evaluated and demonstrated in a number of different applications. The application described in this paper is the assembly of regional jet fuselage panels. Results are presented along with an analysis of the accuracy and repeatability of the system and its elements. [ABSTRACT FROM AUTHOR]