In order to make the task of controlling Mobile-Manipulator Systems (MMS) simpler, a novel command strategy that uses a single joystick is presented to replace the existing paradigm of using multiple joysticks. To improve efficiency and accuracy, virtual fixtures were implemented with the use of a haptic joystick. Instead of modeling the MMS as a single unit with three redundant degrees-of-freedom (DOF), the operator controls either the manipulator or the mobile base, with the command strategy choosing which one to move. The novel command strategy uses three modes of operation to automatically switch control between the manipulator and base. The three modes of operation are called near-target manipulation mode, off-target manipulation mode, and transportation mode. The system enters near-target manipulation mode only when close to a target of interest, and allows the operator to control the manipulator using velocity control. When the operator attempts to move the manipulator out of its workspace limits, the system temporarily enters transportation mode. When the operator moves the manipulator in a direction towards the manipulator’s workspace the system returns to near-target manipulation mode. In off-target manipulation mode, when the operator moves the manipulator to its workspace limits, the system retracts the arm near to the centre of its workspace to enter and remain in transportation mode. While in transportation mode the operator controls the base using velocity control. Two types of virtual fixtures are used, repulsive virtual fixtures and forbidden region virtual fixtures. Repulsive virtual fixtures are present in the form of six virtual walls forming a cube at the manipulator’s workspace limits. When the operator approaches a virtual wall, a repulsive force is felt pushing the operator’s hand away from the workspace limits. The forbidden region virtual fixtures prevent the operator from driving into obstacles by disregarding motion commands that would result in a collision. The command strategy was implemented on the Omnibot MMS and test results show that it was successful in improving simplicity, accuracy, and efficiency when teleoperating a MMS. / UOIT

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Dynamics Simulation Engine is the foundation of the whole system. The engine maintains a realistic dynamics scene in either automatic planning or haptic guided planning. It serves as an off-line verification of the planned motion so that the generated scheme can be 'played' with the engine. In this thesis, we developed a three-dimensional dynamics simulation engine based on an extension of the explicit time-stepping scheme and an application of the differential inclusion process introduced by J. J. Moreau. In the engine, we developed the contact propagation method for a general three-dimensional rigid-body system with multiple unilateral contacts without any bilateral constraints. / In our approach, a sequence of applied forces on the mass center of the workpiece is planned. The applied forces will push the workpiece to get in contact with all the locators. For this purpose, we developed a system with two engines, Motion Planning Engine and Dynamics Simulation Engine. / The goal of Motion Planning Engine is to make the workpiece in contact with all the six locators. Here, the workpiece is initially at an arbitrary place with not contact with any locator. The planning follows a simple scheme of monotonously increase the number of contacts with locators. Here we use a two-step scheme. First, finding the velocity of the workpiece that can approach the new locator while maintaining contacts with old locators. This can be formulated as a linear programming problem. Second, finding the applied force to realize such motion. This step is a central issue in the planning because for the rigid-body model, the solution to multiple frictional contacts is generally indeterministic. One possibility is jamming, that is, the applied force cannot move the workpiece even with less than six contacts. In this thesis, we will give criteria to determine whether the jamming will happen, and we will also derive an algorithm to generate the non-jamming applied force. / The thesis presents an approach to the fixture loading planning problem. That is, to plan the applied forces on the workpiece in order for it to be loaded into a manufacturing fixture. / Liu Tong. / "June 2005." / Adviser: Michael Yu Wang. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4067. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 115-124). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

Tooling design for manufacturing processes refers to direct tooling for making a part such as molds and dies for injection molded parts and metal stampings, or for supporting machining operations such as jigs and fixtures. This paper summarizes some of the R&D activities in those areas over a period of 20 years in the Department of Mechanical Engineering, National University of Singapore. It is notable that increasing use of computer tools has turned what is used to be known as a “black art” into a discipline embracing both heuristic and scientific analyses. / Singapore-MIT Alliance (SMA)

A fixture is a critical link in a machining system. The majority of prior work treats the fixture-workpiece system as quasi-static and ignores the system dynamics. In addition, material removal effect (MRE) on fixture-workpiece dynamics is generally ignored. The primary goal of this thesis is to develop a model-based framework for analysis and synthesis of the fixturing dynamic stability of a machining fixture-workpiece system accounting for the MRE. Five major accomplishments of this thesis are summarized as follows: First, a systematic procedure for analysis of fixturing dynamic stability of an arbitrarily configured machining fixture-workpiece system is developed. Second, models and approaches developed in this work are experimentally validated. It is found that consideration of dynamics and characterization of system dynamic properties are crucial for an accurate analysis. Third, an in-depth investigation of the MRE on fixture-workpiece dynamics is performed. The results show that material removal can significantly change the system characteristics and behavior and approaches developed are capable of capturing the change. Fourth, roles of important fixture design and machining process parameters in affecting fixturing dynamic stability are studied and understood via a parameter effect analysis. Additionally, fixturing dynamic stability is found to be sensitive to the parameter imprecision. Finally, a generic approach for determination of minimum clamping forces that ensure fixturing dynamic stability is developed. Because of MRE, dynamic clamping is found to be an option to achieve the best possible system performance. Models and approaches developed in this thesis are generic and can be used as simulation tools in fixture design. Insights obtained from this research advance the knowledge base of machining fixtures and provide general fixture design guidelines.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Melkote, Shreyes; Committee Member: Liang, Steven; Committee Member: Sitaraman, Suresh.

Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: axiomatic design, case-based reasoning, fixture design, retrieval-by-adaptabilty. Includes bibliographical references (p.273-281).

Les pièces mécaniques fabriquées tel que les feuilles de métal et les pièces à paroi mince, ont souvent des différences géométriques significatives par rapport à leurs modèles CAD nominaux car ils ont une forme considérablement différente dans une condition d’état libre en raison de la gravité et/ou la tension résiduelle. Par conséquence, les fixtures de conformation coûteux sont traditionnellement utilisés pendant les opérations d’inspection géométriques à la phase de contrôle de qualité. L’objective de cette étude est de développer les méthodes d’inspection géométriques automatisées des pièces flexibles qui ne nécessiteraient pas d’utilisation des fixtures. / In manufacturing, quality control (QC) is an essential phase of a product’s lifecycle management (PLM) as it ensures customers receive parts within permissible tolerance ranges and free from defects. Given that all manufactured parts often have geometrical differences compared to their nominal computer-aided design (CAD) models, performing geometrical inspections becomes critical during the QC phase. Nowadays, actual measurements and defect identification during geometrical inspections have been semi-automated through the use of computer-aided inspection (CAI) software. Such software can simplify the inspection into a data acquisition task (contact-based probing or non-contact scanning of the part) followed by semi-automated procedures in a software environment. Despite their growing popularity and practicality, currently available CAI software assume the input acquired data are from a rigid part. This assumption is a major limitation given that not all manufactured parts are rigid, and in some sectors such as the aeronautical industries a considerable percentage of all manufactured components (35 to 40 percent) possess some nonrigid behavior. In other words, CAI software can only be used when a part maintains its shape in both free-state and state-of-use positions. Free-state shape is that which a part has without inspection fixture support and/or before assembly, whilst state-of-use shape is that which is defined in the nominal CAD. Although free-state and state-of-use positions are the same for rigid parts, some mechanical parts such as sheet metals and skins (thin-wall featured parts) often have significantly large geometric deviations in a free-state position compared to their nominal CAD models due to the effects of gravity and residual stress. Referring to such parts as flexible, the aforementioned deviations force the QC technicians to traditionally use a variety of inspection fixtures and conformation jigs in order to maintain flexible parts in their state-of-use position before using conventional CAI software. Without fixation, the free-state elastic geometric deviation of flexible parts would be mistaken by CAI software as plastic deformations and as a result identified as defects. With fixation, the aforementioned free-state deviations are removed before data acquisition, and whatever deviations remain can be inspected as potential defects. However, multiple disadvantages exist in using fixtures including: time consuming set-up process (e.g. 60+ hours for a skin panel in the aerospace industry), considerable purchase and operating expenses, limitations of standard fixture kits in some scenarios, big errors in CAI analysis if fixation has not been conducted correctly, etc. Such disadvantages have recently led researchers to:1) try to circumvent use of fixtures by digitally deforming (or better called registering) the acquired free-state pointcloud/mesh data of a flexible part until it superimposes onto the part’s corresponding nominal CAD model, thereby elastically deforming the data to obtain an optimal state-of-use shape whilst avoiding neutralization of any existing manufacturing defects2) and to try to introduce dedicated defect identification modules with higher degrees of automation (compared to conventional semi-automated CAI tools)In this thesis the same two goals are pursued. A bi-criterion registration method (and two algorithms/demos based upon it) is proposed to achieve the first goal, thereby enabling defect identification of flexible parts in conventional CAI software without the use of fixtures. This is followed by introducing an automated method for fast approximation of defect amplitudes (and an algorithm/demo based upon it) to achieve the second goal. Validation was conducted against a number of virtual (simulated) and experimental industrial case studies. Obtained satisfactory results reflect the effectiveness and utility of the proposed methods.