A CAD/CAM Representation Model Applied to Tolerance Transfer Methods

This paper presents the adaptation of tolerance transfer techniques to a model called TTRS for Technologically and Topologically Related Surfaces. According to this model, any three-dimensional part can be represented as a succession of surface associations forming a tree. Additional tolerancing information can be associated to each TTRS represented as a node on the tree. This information includes dimensional tolerances as well as tolerance chart values. Rules are then established to simulate tolerance chains or stack up along with tolerance charts directly from the graph. This way it becomes possible to combine traditional one dimensional tolerance transfer techniques with a powerful three-dimensional representation model providing high technological contents.

Topology Optimization Algorithm for Plates and Shells Subjected to Plastic Deformations

A topology optimization method for plates and shells subjected to plastic deformations is presented. The algorithms is based on the generalized layout optimization method invented by Bendsϕe and Kikuchi (1988), where an admissible design domain is assumed to be composed of microstructures with periodic cavities. The sizes of the cavities and the rotational angles of the microstructures are design variables which are optimized so as to minimize the applied work. The macroscopic material tensor for the porous material is numerically calculated by the homogenization method for the sensitivity analysis. In this paper, the method is applied to two-dimensional elasto-plastic problems. A database of the material tensor and its interpolation technique are presented. The algorithm is expanded into thin shells subjected to finite deformations. Several numerical examples are shown to demonstrate the effectiveness of these algorithms.

Multirate Integration in Hybrid Electric Vehicle Virtual Proving Grounds

In recent years technology development for the design of electric and hybrid-electric vehicle systems has reached a peak, due to ever increasing restrictions on fuel economy and reduced vehicle emissions. An international race among car manufacturers to bring production hybrid-electric vehicles to market has generated a great deal of interest in the scientific community. The design of these systems requires development of new simulation and optimization tools. In this paper, a description of a real-time numerical environment for Virtual Proving Grounds studies for hybrid-electric vehicles is presented. Within this environment, vehicle models are developed using a recursive multibody dynamics formulation that results in a set of Differential-Algebraic Equations (DAE), and vehicle subsystem models are created using Ordinary Differential Equations (ODE). Based on engineering knowledge of vehicle systems, two time scales are identified. The first time scale, referred to as slow time scale, contains generalized coordinates describing the mechanical vehicle system that includs the chassis, steering rack, and suspension assemblies. The second time scale, referred to as fast time scale, contains the hybrid-electric powertrain components and vehicle tires. Multirate techniques to integrate the combined set of DAE and ODE in two time scales are used to obtain computational gains that will allow solution of the system’s governing equations for state derivatives, and efficient numerical integration in real time.

Applications of Mating Conditions in Assembly Sequence Planning Task

Because of their intuitive interface, mating conditions have been prevalently used in assembly modelling. Besides their use for modelling purposes, other type of information, such as spatial relationships between parts and local degrees of freedom, can be directly derived from mating conditions. This information in turn can be used in various engineering analysis applications, such as kinematics analysis or automatic tolerance chain generation for tolerance analysis. In this paper, application of mating conditions in an assembly sequence-planning task is investigated. The proposed approach mainly engages the mating information represented in the CAD assembly model to automatically generate sequence plans based on the minimization of the number of assembly directions.

Computer Simulation for Ergonomic Bus Operator Workstation Design With Validation

Bus operator’s workstations neglecting ergonomic features can cause overall discomfort and injuries to the users. This paper presents use of JACK®, a human work simulation package, in designing and evaluating a bus operator workstation which can provide sufficient visibility, natural reach, and comfortable posture for operators who range from the 5th percentile female to the 95th percentile male as defined by SAE J833 (SAE, 1994). Three human models representing the two extremes and their medium size person were created and performed 15 bus operating tasks on the bus workstation implemented in JACK®. Kinematic constraints were defined between the human models and the workstation to simulate the tasks in a realistic manner. While the human models simulated the tasks, the body joints were monitored to determine if they exceeded their comfort ranges recommended by Diffrient et al. (1981) and the workstation was evaluated in terms of visibility, reach, comfort, and adjustability. After the workstation design was refined by iterative modifications and the required component adjustment ranges were determined, the workstation design was prototyped into an actual working bus. A jury of bus operators evaluated the workstation design by operating the prototype on a test track. The response from the operators indicated that the workstation would accommodate the intended population.

Assembly Planning: A Genetic Approach

The difficulty of an assembly problem is the inherent complexity of possible solutions. If the most suitable plan is selected after all solutions are found, it will be very time consuming and unrealistic. Motivated by the success of genetic algorithms (GAs) in solving combinatorial and complex problems by examining a small number of possible candidate solutions, GAs are employed to find a near-optimal assembly plan for a general environment. Five genetic operators are used: tree crossover, tree mutation, cut-and-paste, break-and-joint, and reproduction. The fitness function can adapt to different criteria easily. This assembly planner can help an inexperienced technician to find a good solution efficiently. The algorithm has been fully implemented. One example product is given to show the applications and results.

Preparation of a Virtual Proving Ground for Construction Equipment Simulation

A multi-phased evaluation of the Iowa Driving Simulator as a virtual proving ground for construction equipment simulation is presented. In Phase I the Iowa Driving Simulator was evaluated in an “open-loop” mode to assess its capability to simulate a typical maneuver common to wheel loader operation, and its viability as a test platform for human subject evaluation of those maneuvers. A typical wheel loader truck loading cycle involves numerous directional shifts. Cycle productivity is increased if these shifts are executed at full engine throttle. Jerk and acceleration levels associated with full throttle shifts, however, can cause both operator discomfort and spillage of loaded material. Electronically controlled transmissions have the potential to both minimize directional shift times and material loss while optimizing operator comfort. This optimization will require an understanding of the factors which affect operator comfort during shifts. A study was therefore devised to determine those aspects of the motion generated by a directional shift which affect operator comfort. The Iowa Driving Simulator motion system was used to present operators with a series of acceleration time histories which are representative of various shift strategies. The operators rated the relative comfort of each strategy during paired comparison tests. Limitations of the simulator motion system prevented definitive results from being drawn; however, results did confirm shift comfort criteria previously established by the machine manufacturer. Success of the Phase I effort was sufficient to warrant a more in-depth study. In Phase II a complete VPG environment for wheel loader operation on the IDS was developed and qualitatively evaluated. This VPG environment included a visual model of a mine pit, developed for Caterpillar, Inc. by engineers at its National Center for Supercomputing Applications office, combined with the immersive motion capability of the Iowa Driving Simulator. A real-time dynamics model of a generic wheel loader along with a menu driven interface to the data set used to simulate a particular wheel loader were developed at Center for Computer Aided Design. This combination of programs allows changes to the design of a loader to be rapidly evaluated within a virtual proving ground environment or off-line at an engineering workstation. The machine model was then combined with an implement/soil interaction model, also developed at Caterpillar’s National Center for Supercomputing Applications office. The resulting machine model can be evaluated either off-line at a workstation or driven in response to operator input within the Iowa Driving Simulator virtual proving ground environment. A comparison of the offline model’s predictions of machine response to swept-sinewave steering input is shown to compare favorably with measured performance of the actual machine.

Spherical Mechanism Synthesis in Virtual Reality

This paper presents a new approach to using virtual reality (VR) to design spherical mechanisms. VR provides a three dimensional design space where a designer can input design positions using a combination of hand gestures and motions and view the resultant mechanism in stereo using natural head movement to change the viewpoint. Because of the three dimensional nature of the design and verification of spherical mechanisms, VR is examined as a new design interface in this research. In addition to providing a VR environment for design, the research presented in this paper has focused on developing a “design in context” approach to spherical mechanism design. Previous design methods have involved placing coordinate frames along the surface of a constraint sphere. The new “design in context” approach allows a designer to freely place geometric models of movable objects inside an environment consisting of fixed objects. The fixed objects could either act as a base for a mechanism or be potential sources of interference with the motion of the mechanism. This approach allows a designer to perform kinematic synthesis of a mechanism while giving consideration to the interaction of that mechanism with its application environment.

Agent Support for Design of Aircraft Parts

Designing aircraft parts requires extensive coordination among multiple distributed design groups. Achieving such a coordination is time-consuming and expensive, but the cost of ignoring or minimizing it is much higher in terms of delayed and inferior quality products. We have built a multi-agent-based system to provide the desired coordination among the design groups, the legacy applications, and other resources during the preliminary design (PD) process. A variety of agents are used to model the various design and control functionalities. The agent-representation includes a formal representation of the task-structures. A web-based user-interface provides high-level interface to the users. The agents collaborate to achieve the design goals.

Towards Dynamic Tolerance Analysis Using Bond Graphs

A generic method is proposed by which the effect of tolerances in combination with physical effects such as wear can be analysed on the dynamic behavior of mechanisms. The method uses bond graphs in order to simulate the dynamic behavior under the influence of tolerances and other physical effects. The method has the potential to offer enhanced computer support in tolerance value specification as well as in robust design and model based maintenance. The method has partly been implemented using a combination of a geometric modeling system (FROOM) and a bond graph based physical modeling and simulation system (20-Sim).