Vijay Srinivasan

A Portrait of an ISO STEP Tolerancing Standard as an Enabler of Smart Manufacturing Systems

The International Organization for Standardization (ISO) has just completed a major effort on a new standard ISO 10303-242 titled “Managed Model Based 3D Engineering.” It belongs to a family of standards called STEP (STandard for the Exchange of Product model data). ISO 10303-242 is also called the STEP Application Protocol 242 (STEP AP 242, for short). The intent of STEP AP 242 is to support a manufacturing enterprise with a range of standardized information models that flow through a long and wide “digital thread” that makes the manufacturing systems in the enterprise smart. One such standardized information model is that of tolerances specified on a product’s geometry so that the product can be manufactured according to the specifications. This paper describes the attributes of smart manufacturing systems, the capabilities of STEP AP 242 in handling tolerance information associated with product geometry, and how these capabilities enable the manufacturing systems to be smart.

Geometric interoperability via queries

The problem of geometric (model and system) interoperability is conceptualized as a non-trivial generalization of the problem of part interchangeability in mechanical assemblies. Interoperability subsumes the problems of geometric model quality, exchange, and interchangeability, as well as system integration. Until now, most of the interoperability proposals have been data-centric. Instead, we advocate a query-centric approach that can deliver interoperable solutions to many common geometric tasks in computer aided design and manufacturing, including model acquisition and exchange, metrology, and computer aided design/analysis integration.

Technical note: Recent advances in sharing standardized STEP composite structure design and manufacturing information

Composite structures have been developed and used in the aerospace, automobile, sports, and marine industries since the early 1940s. Compared to conventional metallic structures, newer high-performance composite structures provide benefits such as decreased weight and reduced energy consumption. An international standards subcommittee on industrial automation systems and integration has developed and implemented a standard, ISO 10303-209, for sharing the manufacturing information for these complex composite structures. This standard, part of the family of standards commonly known as the Standard for Exchange of Product model data (STEP), is considered essential for improving the design, analysis, and manufacturing productivity of composite structures. The ISO 10303-209 standard also enables the long-term data retention necessary to support the composite structures throughout the lifetime of the products that use them. This paper describes recent advances that led to the development of ISO 10303-209 data models for composite structural shape and composition. The paper also reports the status of ongoing implementation and testing efforts. Varied usage scenarios have motivated several areas for future improvement, such as full three-dimensional representation and the efficient cost-effective visualization of composite structural parts. Issues and their proposed solutions, along with their anticipated impacts on the design, analysis, manufacturing, and long-term support of composite structures are also discussed.

The new frontiers in computational modeling of material structures

We are witnessing the emergence of a new paradigm in the modeling of material structures. It stems from the digitization of manufacturing and is fueled by advances in additive manufacturing and material science. This paper strives to provide a critical examination of this new paradigm in a historical and technological context and to show that it requires non-trivial extensions and generalizations of the classical theoretical foundation and algorithmic solutions originally developed for solid modeling. Specifically, it requires new models and data-intensive representations for materials, physical behavior, and manufacturing processes across multiple scales. In particular, we argue that most computational tasks that support traditional and emerging manufacturing may be formulated systematically and addressed in terms of relations (conversions, synthesis, change propagation updates, verification, and other harmonization activities) among four views (manifestations) of an engineered artifact: Functional, which captures the design constraints and tolerances on shape, properties, and behavior; Designed, which represents a toleranced design that satisfies these constraints; Planned, which defines a manufacturing process plan; Simulated, which models the expected outcome of the process plan; and a Real sample set of physical artifacts produced by executing the process plan on a particular manufacturing technology. Based on this formulation, we outline important directions for a research agenda aimed at enabling, driving, and amplifying further advances in digital design and manufacturing. Display Omitted

Reflections on the role of science in the evolution of dimensioning and tolerancing standards

Dimensioning and tolerancing standards originated about 75 years ago in the form of various national and company standards that governed engineering draughting and documentation practices. They served the purpose of communicating to manufacturers what geometric variations designers could tolerate in a product without compromising the product’s intended function. These standards have evolved over time and are by now well entrenched in the engineering profession throughout the world. For several initial decades, this evolution was driven primarily by codification of best engineering practices without the benefit of any systematic scientific treatment. This trend encountered a major hurdle in early 1980s when the emergence of computer-aided design and manufacturing systems forced a drastic reexamination of these standards with a greater emphasis on mathematical formalism. Since then, scientific principles to explain past practices and to guide future evolution have emerged, and the role of science has now become more prominent in the development of these standards. This article describes some of the key scientific research results that have already had an impact, and the future scientific trends that are likely to have an influence, on these evolving standards.

Trust-based multi-agent filtering for increased Smart Grid security

We address the problem of state estimation of the power system for the Smart Grid. We assume that the monitoring of the electrical grid is done by a network of agents with both computing and communication capabilities. We propose a security mechanism aimed at protecting the state estimation process against false data injections originating from faulty equipment or cyber-attacks. Our approach is based on a multi-agent filtering scheme, where in addition to taking measurements, the agents are also computing local estimates based on their own measurements and on the estimates of the neighboring agents. We combine the multi-agent filtering scheme with a trust-based mechanism under which each agent associates a trust metric to each of its neighbors. These trust metrics are taken into account in the filtering scheme so that information transmitted from agents with low trust is disregarded. In addition, a mechanism for the trust metric update is also introduced, which ensures that agents that diverge considerably from their expected behavior have their trust values lowered.

On Architecting and Composing Engineering Information Services to Enable Smart Manufacturing

Engineering information systems play an important role in the current era of digitization of manufacturing, which is a key component to enable smart manufacturing. Traditionally, these engineering information systems spanned the lifecycle of a product by providing interoperability of software subsystems through a combination of open and proprietary exchange of data. But research and development efforts are underway to replace this paradigm with engineering information services that can be composed dynamically to meet changing needs in the operation of smart manufacturing systems. This paper describes the opportunities and challenges in architecting such engineering information services and composing them to enable smarter manufacturing.

Opinion: Report from a 2013 ASME panel on geometric interoperability for advanced manufacturing

During the Summer of 2013 in a conference organized by the American Society of Mechanical Engineers (ASME) at Madison, Wisconsin, a panel of academic, industrial, and government researchers engaged in a spirited discussion on the issue of geometric interoperability for advanced manufacturing.1 It was set in the background of heightened anxiety in various Western countries about the relative decline in their manufacturing activity and keen interest in reviving it through research and development. The Government of the United Kingdom, for example, has recently created several centers for innovativemanufacturing.2 TheUSGovernment has already set up a National Additive Manufacturing Innovation Institute,3 and is poised to set up several more such national institutes to spur manufacturing innovation. While the challenges these countries and their institutes face have several dimensions, the ASME panel focused on a particularly nagging technical problem of geometric interoperability that is plaguing the progress in many advanced manufacturing systems, tools and technologies. The panelists had considerable experience in the use of geometry in various design and manufacturing functions in industry. In spite of the widespread use of geometry throughout the lifespan of a manufactured product, it is the Computer-Aided Design (CAD) systems that serve as the dominant source for the geometric information needed in all modern Product LifecycleManagement (PLM) systems. Current CAD systems are built on the geometric and solid modeling foundations initially laid nearly 40 years ago. As the panelists described some of the industrial problems in advanced manufacturing and how they were solving them, it became clear that they are resorting to various ‘workarounds’ in the CAD-initiated representations of geometric information. The manufacturing of layered composite structures serves as an interesting and useful example of advanced manufacturing. It has all the elements that illustrate the challenges faced by modern

Size tolerancing revisited: A basic notion and its evolution in standards:

Size is a fundamental descriptor of objects—it allows us to quantify “how big” objects are and to compare and classify objects based on this notion. In the world of International Organization for Standardization Geometrical Product Specification and Verification, size is defined much more narrowly: it is restricted to features of size, and the methods of inducing size values from an actual workpiece are strictly controlled. The release of ISO 14405-1:2010 has introduced a rich new set of size specification modifiers, which includes two-point and spherical local sizes, least squares, maximum inscribed and minimum circumscribed associations, as well as calculated diameters (inferred from the circumference, area, or volume of the feature of interest). Further modifiers allow the specification of statistics of local size measurements, such as maximum, minimum, range, average, and others. This article will present “size” as a fundamental engineering notion from several viewpoints and trace its evolution in engineering drawings. It will then discuss the implications of the use of the recently standardized size modifiers in engineering design and investigate the issues that may arise in the application and interpretation of these extensions to size.

Theory and Algorithms for Weighted Total Least-Squares Fitting of Lines, Planes, and Parallel Planes to Support Tolerancing Standards

We present the theory and algorithms for fitting a line, a plane, two parallel planes (corresponding to a slot or a slab), or many parallel planes in a total (orthogonal) least-squares sense to coordinate data that is weighted. Each of these problems is reduced to a simple 3 � 3 matrix eigenvalue/eigenvector problem or an equivalent singular value decomposition problem, which can be solved using reliable and readily available commercial software. These methods were numerically verified by comparing them with brute-force minimization searches. We demonstrate the need for such weighted total least-squares fitting in coordinate metrology to support new and emerging tolerancing standards, for instance, ISO 14405-1:2010. The widespread practice of unweighted fitting works well enough when point sampling is controlled and can be made uniform (e.g., using a discrete point contact coordinate measuring machine). However, we show by example that nonuniformly sampled points (arising from many new measurement technologies) coupled with unweighted least-squares fitting can lead to erroneous results. When needed, the algorithms presented also solve the unweighted cases simply by assigning the value one to each weight. We additionally prove convergence from the discrete to continuous cases of least-squares fitting as the point sampling becomes dense. [DOI: 10.1115/1.4024854]