30,434 research outputs found
12th CIRP Conference on Computer Aided Tolerancing
The purpose of this paper is to decipher the process of modelling driving to the product behaviour simulation. A simple example of simulation, tolerance stackup, allows illustrating this process. The tolerance stackup is used daily in industry, however, designers do they know exactly what they do? Are they aware of the assumptions they are introducing? To answer to these questions, concepts of GeoSpelling and of GPS ISO standards such as skin model, operations, operators and other concept are introduced such as finite and infinite models
Validation of Ultrahigh Dependability for Software-Based Systems
Modern society depends on computers for a number of critical tasks in which failure can have very high costs. As a consequence, high levels of dependability (reliability, safety, etc.) are required from such computers, including their software. Whenever a quantitative approach to risk is adopted, these requirements must be stated in quantitative terms, and a rigorous demonstration of their being attained is necessary. For software used in the most critical roles, such demonstrations are not usually supplied. The fact is that the dependability requirements often lie near the limit of the current state of the art, or beyond, in terms not only of the ability to satisfy them, but also, and more often, of the ability to demonstrate that they are satisfied in the individual operational products (validation). We discuss reasons why such demonstrations cannot usually be provided with the means available: reliability growth models, testing with stable reliability, structural dependability modelling, as well as more informal arguments based on good engineering practice. We state some rigorous arguments about the limits of what can be validated with each of such means. Combining evidence from these different sources would seem to raise the levels that can be validated; yet this improvement is not such as to solve the problem. It appears that engineering practice must take into account the fact that no solution exists, at present, for the validation of ultra-high dependability in systems relying on complex software
Control/structure interaction design methodology
The Control Structure Interaction Program is a technology development program for spacecraft that exhibit interactions between the control system and structural dynamics. The program objectives include development and verification of new design concepts (such as active structure) and new tools (such as a combined structure and control optimization algorithm) and their verification in ground and possibly flight test. The new CSI design methodology is centered around interdisciplinary engineers using new tools that closely integrate structures and controls. Verification is an important CSI theme and analysts will be closely integrated to the CSI Test Bed laboratory. Components, concepts, tools and algorithms will be developed and tested in the lab and in future Shuttle-based flight experiments. The design methodology is summarized in block diagrams depicting the evolution of a spacecraft design and descriptions of analytical capabilities used in the process. The multiyear JPL CSI implementation plan is described along with the essentials of several new tools. A distributed network of computation servers and workstations was designed that will provide a state-of-the-art development base for the CSI technologies
Modeling of 2D and 3D Assemblies Taking Into Account Form Errors of Plane Surfaces
The tolerancing process links the virtual and the real worlds. From the
former, tolerances define a variational geometrical language (geometric
parameters). From the latter, there are values limiting those parameters. The
beginning of a tolerancing process is in this duality. As high precision
assemblies cannot be analyzed with the assumption that form errors are
negligible, we propose to apply this process to assemblies with form errors
through a new way of allowing to parameterize forms and solve their assemblies.
The assembly process is calculated through a method of allowing to solve the 3D
assemblies of pairs of surfaces having form errors using a static equilibrium.
We have built a geometrical model based on the modal shapes of the ideal
surface. We compute for the completely deterministic contact points between
this pair of shapes according to a given assembly process. The solution gives
an accurate evaluation of the assembly performance. Then we compare the results
with or without taking into account the form errors. When we analyze a batch of
assemblies, the problem is to compute for the nonconformity rate of a pilot
production according to the functional requirements. We input probable errors
of surfaces (position, orientation, and form) in our calculus and we evaluate
the quality of the results compared with the functional requirements. The pilot
production then can or cannot be validated
Task Specific Uncertainty in Coordinate Measurement
Task specific uncertainty is the measurement uncertainty associated with the measurement of a specific feature using a specific measurement plan. This paper surveys techniques developed to model and estimate task specific uncertainty for coordinate measuring systems, primarily coordinate measuring machines using contacting probes. Sources of uncertainty are also reviewed
Production of Reliable Flight Crucial Software: Validation Methods Research for Fault Tolerant Avionics and Control Systems Sub-Working Group Meeting
The state of the art in the production of crucial software for flight control applications was addressed. The association between reliability metrics and software is considered. Thirteen software development projects are discussed. A short term need for research in the areas of tool development and software fault tolerance was indicated. For the long term, research in format verification or proof methods was recommended. Formal specification and software reliability modeling, were recommended as topics for both short and long term research
Robust Satisfaction of Temporal Logic Specifications via Reinforcement Learning
We consider the problem of steering a system with unknown, stochastic
dynamics to satisfy a rich, temporally layered task given as a signal temporal
logic formula. We represent the system as a Markov decision process in which
the states are built from a partition of the state space and the transition
probabilities are unknown. We present provably convergent reinforcement
learning algorithms to maximize the probability of satisfying a given formula
and to maximize the average expected robustness, i.e., a measure of how
strongly the formula is satisfied. We demonstrate via a pair of robot
navigation simulation case studies that reinforcement learning with robustness
maximization performs better than probability maximization in terms of both
probability of satisfaction and expected robustness.Comment: 8 pages, 4 figure
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