Ajay Joneja

Protrusion-features handling in design and manufacturing planning

Abstract In a feature-based design system, a designer should be able to design with both protrusion and depression features. Since depression features loosely correspond to machining processes, they are easy to handle during process planning and NC cutter-path generation. However, the same cannot be said for protrusion features. Not only do the removal volumes surrounding the feature need to be extracted into depression features, but the original workpiece needs to increase in size so that there is enough material for the protruding features. A backward-growing methodology for handling protrusion features for process planning is discussed. Its implementation in an integrated design/ manufacturing system called QTC II is described.

Tool path optimization in layered manufacturing

Abstract There are several manufacturing applications in which a tool needs to move along a prescribed path performing machining operations. The path is typically described by a sequence of curves. For the entire process, the tool must move along each curve exactly once. For typical paths, significant time may be wasted in the movement between the end point of one curve to the start vertex of the next one along which the tool must operate. Normally, this non-machining motion is a straight-line motion. A good process plan would minimize the time wasted on such motion. An excellent application of this problem is found in the increasingly popular Layered Manufacturing (LM) methods. We first introduce a Genetic Algorithm (GA)-based approach to solve this problem. Next, we present a new strategy using a combination of the Asymmetric Traveling Salesman Problem and Integer Programming (TSP-IP) to solve it. Based on the pros and cons of these approaches, two enhanced GA formulations are developed. We compare the performance of the different techniques, with a view to their application to real-time path planning in LM applications.

HIGH-RESOLUTION MULTIDIMENSIONAL DISPLACEMENT MONITORING SYSTEM

The possibility of using quadrant detectors to develop a new optical system that can monitor all six degrees of freedom of mechanical workpieces with very high resolution is investigated. A prototype system based on this approach has been designed and built. Although the system is not fully optimized, our proposed system has already demonstrated some promising results. Using a thermally compensated laser source together with a pinhole spatial filtering system, we have demonstrated that lateral resolution better than 50 nm and angular displacement resolution better than 0.25 ?rad is achievable with this system.

Technical Section: Sketch-based free-form shape modelling with a fast and stable numerical engine

In this paper, we present a feature-based free-form shape modelling technique based on solving a fundamental problem of reconstructing the depth information from 2D sketch planes. First, to mathematically define the problem with the human perception, the proposed technique (1) formulates the 2D shaded regions on sketches by a hybrid thin plate surface model that can exhibit controlled continuity over the recovered 3D surface and (2) formulates the 1D salient open free-form curves and salient corners as linear sketch constraints. The 3D free-form shape from sketch planes is then achieved by solving a linearly constrained quadratic optimization problem which unifies both 2D region-based and 1D contour-based shape information over 2D sketches. Secondly, to solve the formulated optimization problem with an interactive-rate performance, a fast and stable numerical engine is proposed with a rigorous proof that for our specially formulated problem, system decomposition with reduced computational cost is always possible. Stability, accuracy and efficiency are studied in depth for the proposed numerical engine. Finally a prototype system utilizing the proposed technique is presented with two applications that demonstrate the usefulness and effectiveness of the proposed technique.

Automated configuration of parametric feeding tools for mass customization

Abstract Mass customization is a dominant new trend in modern manufacturing, where by industries are required to produce umpteen variations of products at costs approaching those achievable in mass production. Among the methods to tackle this demand is development of flexible tooling which operates at high throughput rates. A suite of such tools called MPATS (a Modular, Parametric, Assembly Tool Set) is developed for this. The paper introduces MPATS, and also describes a computer-aided planning system to automatically configure MPATS.

Modeling dynamic developable meshes by the Hamilton principle

In this paper, a new dynamic developable surface model is proposed. The proposed model represents developable surfaces using triangle meshes. A novel algorithm is proposed to introduce the Hamilton principle into these meshes such that the resulting developable model is dynamic, i.e., it can offer a time-dependent continuous path to deform the model. Applications with examples are presented; these show that the proposed technique can model buckled developable surfaces well, and can offer physically-realistic animations of deformed developable surfaces.

Modeling wrinkles on smooth surfaces for footwear design

We describe two new shape operators that superimpose wrinkles on top of a smooth NURBS surface. Previous research studying wrinkles focused mostly on cloth modeling or in animations, which are driven more by visual realism, but allow large elastic deformations. Our operators generate wrinkle-shaped deformations in a region of a smooth surface along a given boundary based on a few basic parametric inputs such as wrinkle magnitude and extent (these terms will be defined in the paper). The essential geometric transformation to map the smooth surface to a wrinkled one will be defined purely in terms of the geometry of the surface and the input parameters. Our model is based on two surface properties: geodesic offsets and surface energy. Practical implementation of the operators is discussed, and examples presented. Finally, the motivation for the operators will be given through their application in the computer-aided design and manufacture of footwear.

Path Generation for High Speed Machining Using Spiral Curves

AbstractAs high speed machining is becoming more and more important in modern machines shops, generating efficient cutter path for high speed machining is highly desirable. For this type of path, it should have the least number of sharp turns as well as the second derivatives along the path is controllable is preferred. Archimedean spirals have no sharp turn, and the step-over between adjacent segments can also be controlled to a predefined value. A clothoid spiral has the property that the second derivative varies linearly with the length of the curve. Therefore, these spiral curves can be used to generate paths with constant cutter engagement values as well as maintain smooth movements while performing cornering and linking movements. In this paper, we will introduce a detailed approach which covers a 2D region in a very efficient manner by using the combination of Archimedean and clothoid spirals.

A modular, parametric vibratory feeder: a case study for flexible assembly tools for mass customization

A new class of parametric and modular flexible tools is proposed to improve the setup times of assembly lines. The methodology is especially effective in dealing with problems of mass customization. In addition to improvements in the setup time, the methodology, MPATS (modular, parametric assembly tool sets) has other potential advantages such as lower tooling costs as well as faster tooling lead times compared to conventional assembly systems utilizing custom made tools. To demonstrate the feasibility of the methodology, a prototype tool set is designed and presented in this paper. The prototype tool set focuses on the most common of feeding and orienting tools: vibratory bowl feeders.

Traversing the machining graph of a pocket

Abstract A simple and linear-time algorithm is presented for solving the problem of traversing a machining graph with minimum retractions encountered in zigzag pocket machining and other applications. This algorithm finds a traversal of the machining graph of a general pocket P with Nh holes, such that the number of retractions in the traversal is no greater than OPT+Nh+Nr, where OPT is the (unknown) minimum number of retractions required by any algorithm and Nr is the number of reducible blocks in P (to be defined in the paper). When the step-over distance is small enough relative to the size of P, Nr becomes zero, and our result deviates from OPT by at most the number of holes in P, a significant improvement over the upper bound 5OPT+6Nh achieved [Proceedings of the Seventh ACM-SIAM Symposium on Discrete Algorithms, 1996; Algorithmica 2000 (26) 19]. In particular, if Nh is zero as well, i.e. when P has no holes, the proposed algorithm outputs an optimal solution. A novel computational modeling tool called block transition graph is introduced to formulate the traversal problem in a compact and concise form. Efficient algorithms are then presented for traversing this graph, which in turn gives rise to the major result.