Planar Cable-Direct-Driven Robots: Part II — Dynamics and Control

A hybrid parallel/serial manipulator architecture was introduced in a companion paper where the translational freedoms are provided by a cable-direct-driven robot (CDDR) and the rotational freedoms are provided by a serial wrist mechanism. While the companion paper presents kinematics and statics, the current paper presents a dynamics model and simulated control for planar CDDRs. Examples are presented to compare the planar 3-cable CDDR with one degree of actuation redundancy and the 4-cable CDDR with two degrees of actuation redundancy. It was found that the 4-cable tracking error was worse than for the 3-cable case, due to increased inertia with an additional actuator. Also, the controller architecture considers including and not including a feedforward reference acceleration term with the overall mass matrix; the performance of the controller with the feedforward term is clearly preferable.

Optimization of the Closure-Weld Region of Cylindrical Containers for Long-Term Corrosion Resistance

Welded cylindrical containers usually experience stress corrosion cracking (SCC) in the closure-weld area. Induction coil heating technique may be used to relieve the residual stresses from the closure-weld. This technique involves localized heating of the material by the surrounding coils. The material is then cooled to the room temperature by quenching. A two-dimensional axisymmetric finite element model is developed to study the effects of induction coil heating and subsequent quenching. The finite element results are validated through an experimental test. The parameters of the design are tuned to maximize the compressive stress within a layer of thickness from the outer surface that is equal to the long-term general corrosion of Alloy 22 (Appendix A). The problem is subject to geometrical and stress constraints. Two different solution methods are implemented for this purpose. First, an off-the-shelf optimization software is used to obtain an optimum solution. These results are not satisfactory because of the highly nonlinear nature of the problem. The paper proposes a novel alternative: the Successive Heuristic Quadratic Approximation (SHQA) technique. This algorithm combines successive quadratic approximation with an adaptive random search. Examples and discussion are included.

Material Instrumentation: A Crystallization of Different Points of View in the Multi-Trade Product Design: A Visual and Tactile Field Application

The topic of this article is to consider the role of material instrumentation in inter-trade cooperation and innovation dynamics. Within today’s competition context, innovation and knowledge management concern more and more products design. Various actors come into account during product design phase. We can quote designers, ergonomist, technologist and marketer: as many competence and different visions. In the first part, we will endeavour to show in what material instrumentation can stimulates the inter-trade cooperation. Then through a concrete example, we will endeavour to show how material instrumentation is supported by innovation.

Tool Path Generation Based on B-Spline Wavelets

Tool path generation is a fundamental problem in numerical control machining. Typical methods used for machining 2.5D objects include generation of offset contours using trimmed offset curves and zigzag sequences. The offset contours result in unnecessary detailed curves far away from the object boundary. The zigzag sequences result in frequent stops and changes in tool direction. In this paper we present a novel approach for tool path generation based on wavelet theory. The theory of wavelets naturally leads to a simple cut sequence algorithm that provides valid and efficient coverage of the machined surface. The classical analytical and algebraic complexity in tool path planning is also reduced. In this paper, curves are represented by endpoint interpolating B-splines and their corresponding wavelets. Design and manufacturing examples are also presented in this paper.

A Finite Element Approach to Direct Surface Manipulation

Direct surface manipulation (DSM) allows a designer to add a raised or indented feature to an existing NURBS or finite element surface. The user bounds the feature with a closed curve, and indicates an influence center that represents either the highest or lowest area of the feature. As we move radially outward from the influence center to the boundary curve, the magnitude of displacement is scaled gradually by a 1D parametric cubic basis function whose values range from 0 to 1. In this paper we present a new technique for assigning parameter values in the radial direction, i.e. u, to points within a DSM feature. The new technique poses parameter distribution as a Dirichlet problem and uses a finite element method to solve for u(x,y). The new method overcomes some stringent geometric conditions inherited from a fundamentally geometric-based reparameterization scheme and allows us to work with non-star-shaped and multiply-connected DSM features. Thus it allows us to apply this surface feature technique to a wider variety of surface applications.

A Multi-Project Management Approach for Distributed Projects Management

As planning is the action undertaken before execution, it has a great importance as every investment. We identify some problematics in the planning process, and give some lightings about how to make it more efficient and reliable. We propose some methods for managing project at each detail level. We propose the extension of project manager’s concepts to all the people who are accountable for some objective or deliverable. So, there are in a single project a lot of people managing the part they are responsible for as an entire project. We propose a standard methodological kit for them, and we describe the consequences on skills and responsibilities of the project actors, and on the decisions they have to take and efforts they have to undertake to reach their objectives.

Promoting Modularity in Evolutionary Design

Evolutionary design systems apply principles inspired from biological evolution to automate machine design. These systems have been shown to generate simple designs for simple tasks — but their practical ability to scale up to higher complexities remains questioned. One of the keys to accomplishing higher-level evolutionary design is the ability of the process to identify and reuse knowledge discovered at lower levels, thus scaling its search capacity. One way to capture this knowledge is in the form of reusable building blocks — modules. In this paper we define modularity and discuss several approaches to promoting modularity in evolutionary design systems. In particular, we propose a new mechanism that can enhance modularization. This mechanism is based on the observation that designs that exhibit modularity have higher adaptability and consequently have better survival rates under changing requirements. Contrary to other techniques, this is a weak (indirect) formulation that docs not require representation of partial solutions or definition of a genotype from which a design is developed. We demonstrate this principle on an abstract general design problem on which modularity can be statistically quantified.

Support Structures Extraction for Hybrid Layered Manufacturing

In a multi-axis metal hybrid layered manufacturing system, a combined laser material deposition and material removal system with more than 3-aixs mobility, sometimes support structures are necessary in the part building process, which prevent object from falling during deposition process. Since the support material is the same as build material, it is very difficult to remove the support material in the post processing stage. Thus, the support material must be machined off. Therefore, the geometry information of support structures is important for the machining process. In this paper, a method is presented to extract support structures automatically. Two types of support structures, trapped and non-trapped, are classified in this paper and their extraction methods are discussed respectively.

Effective Generation of Pareto Sets Using Genetic Programming

Many designers concede that there is typically more than one measure of performance for an artifact. Often, a large system is decomposed into smaller subsystems each having its own set of objectives, constraints, and parameters. The performance of the final design is a function of the performances of the individual subsystems. It then becomes necessary to consider the tradeoffs that occur in a multi-objective design problem. The complete solution to a multi-objective optimization problem is the entire set of non-dominated configurations commonly referred to as the Pareto set. Common methods of generating points along a Pareto frontier involve repeated conversion of multi-objective problems into single objective problems using weights. These methods have been shown to perform poorly when attempting to populate a Pareto frontier. This work presents an efficient means of generating a thorough spread of points along a Pareto frontier using genetic programming.

Tuning a Hybrid Optimization Algorithm by Determining the Modality of the Design Space

In this paper we present an approach for increasing the efficiency of a hybrid Genetic/Sequential Linear Programming algorithm. We introduce two metrics for evaluating the modality of the design space and then use this information to efficiently switch between the Genetic Algorithm and SLP algorithm. The motivation for this study is an effort to reduce the computational expense associated with the use of a Genetic Algorithm by reducing the number of function evaluations needed to find good solutions. In the paper the two metrics used to evaluate the modality of the design space are the variance in fitness of the population of the designs in the Genetic Algorithm and the error associated with fitting a response surface to the designs evaluates by the Genetic Algorithm. The effectiveness of this approach is demonstrated by considering a highly multimodal Genetic Algorithm benchmarking problem.