Mahadevan Balasubramaniam

Generating 5-axis NC roughing paths directly from a tessellated representation

We describe a system that generates 5-axis roughing tool paths directly from a tessellated representation of a body. Instead of decomposing the shape into manufacturing primitives, we generate tool paths directly from the shape of the workpiece using measures of accessibility avoid collisions. There are three stages in our approach: visibility computation, posture definition and path interpolation. In the first stage, we use the concept of visibility to determine the directions from which a point in the delta-volume is likely to be accessible to an observer located outside the convex envelope of the object and describe a technique to compute this information rapidly using graphics hardware. However, visibility does not ensure accessibility because visibility cannot account for the diameter of the tool, the tool-holder or the spindle. In the posture definition stage, a local search is performed in the neighborhood of the visibility direction using rapid collision avoidance. The output of this step is a set of valid tool postures for every sample point in the delta-volume. Finally, all that remains to be done is to connect the valid postures into a valid continuous tool path. This is not a trivial task because the tool must not interfere with the part while interpolating between valid postures. In the third stage of our approach we interpolate collision free tool paths by performing NC simulation and path correction within the loop of path generation using rapid collision detection algorithms.

Collision-free finishing toolpaths from visibility data

We present a series of algorithms and heuristics for generating collision-free 5-axis CNC finishing toolpaths automatically. These algorithms are based on the core concept of visibility, which can be generated in high resolution by discretizing the part and using graphics hardware as described in earlier papers by the authors. Using this visibility data for finish machining is a challenge, and we show how it can be used to generate globally collision-free 5-axis finishing toolpaths while also considering machine limits, tool tilt, cusp height limits, tool pitch limits and the need to keep toolpaths continuous. We then show how the toolpath can be verified during the path generation process, how collision-free interpolation can be carried out and how the sampling can be adjusted to ensure that the finishing toolpaths are accurate. We end with examples of 5-axis toolpaths generated for complex parts.

Generation of collision-free 5-axis tool paths using a haptic surface

Abstract An intuitive man–machine interface for generating 5-axis tool paths is described in the paper. The system is based on a 5 degree-of-freedom force feedback haptic system, which is used to interface a human with an impenetrable 3D part. In the process of feeling the object, the user ‘teaches’ a milling machine to machine a virtual 3D object. The tool path generation has two phases: recording of access directions at the surface of the object and the post-processing phase. During the recording phase, three functions are carried out simultaneously: first, a fast collision detection algorithm, using hierarchical object representation, to drive the haptic system; second, visual feedback to show the regions that have been accessed by the tool; and third, a system to capture the access directions of the tool as the user touches the object. The post-processing phase involves the use of information generated in the recording phase to generate 5-axis tool paths. First, the access directions at the surface of the part are interpolated; and second, any residual collisions are detected and eliminated. We show the results of the tool path generation for two parts. The system can help an expert user generate, correct and tweak tool paths.

Tool selection in three-axis rough machining

An approach to tool selection and sequencing is presented for three-axis rough machining. The trade-off in the selection of tools is as follows: larger tools have reduced access while smaller tools are capable of reduced cutting speed. Furthermore, every tool change incurs a time penalty. The objective of this paper is to select a tool sequence that minimizes the total rough-machining time. In our approach, the removal volume is stratified into 2.5D machining slabs and, for each tool, the area accessible in each slab is computed incrementally, keeping in mind the cutting portion of the tool and the shape of the tool holder and spindle assembly. This reduces the three-axis problem to a series of two-axis problems with complex precedence constraints. Two models are presented to understand this new form of the problem. First, an integer linear programming formulation is discussed to show the complexity of the task. Second, a network flow formulation is presented, by which we show that it is possible to obtain efficiently an approximate solution of the problem. Examples are discussed to illustrate the algorithms discussed.

An anti-backlash two-part shaft coupling with interlocking elastically averaged teeth

A new family of compliant and self-locking tapered torsional couplings have been developed as an alternate to spline-type couplings. The couplings use designed compliance to ensure constant contact between mating beam-like teeth. The tip of one tooth is larger, but tapered, so that when it mates at the base of the opposed tooth, it deflects radially. The taper is self-locking to prevent radial deflection under torsional load. This eliminates backlash between parts while maintaining a relatively high torsional stiffness. The large number of mating teeth elastically average errors in the teeth.

Optical fiber reliability in subsea monitoring

Fiber optic cables have been successfully deployed in ocean floors for decades to enable trans-oceanic telecommunication. The impact of strain and moisture on optical fibers has been thoroughly studied in the past 30 years. Cable designs have been developed to minimize strain on the fibers and prevent water uptake. As a result, the failure rates of optical fibers in subsea telecommunication cables due to moisture and strain are negligible. However, the relatively recent use of fiber optic cables to monitor temperature, acoustics, and especially strain on subsea equipment adds new reliability challenges that need to be mitigated. This paper provides a brief overview of the design for reliability considerations of fiber optic cables for subsea asset condition monitoring (SACM). In particular, experimental results on fibers immersed in water under varying accelerated conditions of static stress and temperature are discussed. Based on the data, an assessment of the survivability of optical fibers in the subsea monitoring environment is presented.

Inverse Modeling Techniques for Application to Engine Transient Performance Data Matching

A framework demonstrating the application of inverse modeling technology for engine performance data matching is presented. Transient aero-thermodynamic cycle models are used to simulate engine performance and control characteristics over the entire flight envelope. These models are used not only for engine design and certification but also to provide performance guarantees to the customer and for engine diagnostics. Therefore, it is extremely important that these models are able to accurately predict the performance metrics of interest. Accuracy of these models can be improved by fine-tuning model parameters so that the model output best matches the flight test data. The performance of an aircraft engine is fine tuned from several sensor observations, e.g. exhaust gas temperature, fuel flow, and fan speed. These observations vary with parameters like power level, core speed and operating conditions like altitude, inlet conditions (temperature and pressure), and Mach number, and are used in conjunction with a transient performance simulation model to assess engine performance. This is normally achieved through an iterative manual approach that requires a lot of expert judgment. Simulating transient performance characteristics often requires an engineer to estimate model parameters by matching model response to engine sensor data. Such an estimation problem can be posed using inverse modeling technology. One of the main challenges in the application of inverse modeling for parameter estimation is that the problem can be ill-posed that leads to instability and non-uniqueness of the solution. The inverse method employed here for parameter estimation provides a solution for both well-posed and ill-posed problems. Sensitivity analysis can be used to better pose the data-matching problem. Singular value decomposition (SVD) technique is used to address the ill-posed nature of the inverse problem, which is solved as a finite dimensional non-linear optimization problem. Typically, the transient response is highly nonlinear and it may not be possible to match the whole transient simultaneously. This paper extends the framework on transient inverse modeling developed in [1] for engine transient performance applications. Variable weighting mechanism allows providing different weights to different sensors. This helps in better control on data matching, identify drift in parameter values over time, and point towards incorrect modeling assumptions. The application of the inverse methodology is demonstrated on a single spool non-afterburning engine and a commercial aviation engine model.Copyright

Inverse Modeling Technology For Transient Engine Performance Data Matching

The paper develops a framework for application of inverse modeling techniques to develop accurate simulation models for aircraft engine performance characteristics. Typically, the performance of an aircraft engine is fine tuned from several sensor observations, e.g. exhaust gas temperature, fuel flow and fan speed. These observations vary with parameters like power level, core speed and operating conditions like ambient temperature, pressure and MACH number, and are used in conjunction with a transient performance simulation model to assess engine performance. Transient aero-thermodynamic cycle models have been developed to simulate engine performance and control characteristics over the entire flight envelope. Accuracy of these models can be improved by fine-tuning model parameters so that the model output best matches the flight test data. The application of inverse modeling for parameter estimation for transient data matching is challenging for two reasons. Firstly, the problem can be ill posed leading to instability and non-uniqueness of the solution. The Singular Value Decomposition (SVD) technique employed in this paper for parameter estimation provides a solution for both well-posed and ill-posed inverse problems, which is solved as a finite dimensional non-linear optimization problem [1]. Secondly, the transient response of an engine is highly non-linear and it may not be possible to match the entire transient regime accurately with a given set of model parameters. The transient weighting capability developed in this paper overcomes this difficulty by doing selective data matching over a specified region of interest. The application of the inverse methodology is demonstrated on a single spool non-afterburning engine and other aviation engine models.

Some Theory and Algorithms Pertaining to Machinability and Visibility

In previous work, we and others have developed visibility-based tool path generation schemes. Almost all previous research implicitly assumes that all visible parts are machinable. Though usually true practice, this assumption hides several subtleties inherent to the geometry of the machining process. Here, we define machinability in a stricter sense, as a generalization of the robotic path planning problem. Then, we define various “tight” necessary conditions for strict machinability, and show the connections between these conditions. After demonstrating the richness of the information contained in visibility, we show how to compute visibility effectively. Visible directions constitute an approximate feasible configuration space of a cutting tool. We also address questions pertaining to the topological connectivity of the feasible space. The theoretical results of this paper lay down a firmer foundation of machining path planning.© 2002 ASME

Dynamic analysis of two types of over-crank guillotine shears—a comparative study

Two models of guillotine shearing machines, one with the drive shaft parallel to the blade and the other with the drive shaft perpendicular to the blade are considered. These machines experience both static and dynamic loading while the shear is in operation. The magnitude of the stress at any location changes as the cutting progresses from one point to another. The main aim of this paper is to compare the static behaviour of the two machines with respect to strength, rigidity and weight, vibrational characteristics and dynamic behaviour under identical operating conditions.