Tomohisa Tanaka

An 8-Axis Robot Based Rough Cutting System for Surface Sculpturing

In this paper, a rough cutting system for surface sculpturing is proposed. The 8-axis machining system is composed of a 6-axis robot and a 2-axis worktable. It carves block of polystyrene foam by hotwire. According to the geometric feature, the system automatically simplifys the input model into a user specified resolution and generates a series of rough cutting models which are composed of large, flat faces. Then according to the cutting tool path generated by the path-planning algorithm, the rough cutting model is sculptured face by face.

Optimization of Multipass Turning Parameters by Genetic Algorithm

Optimization of cutting parameters is one of the key obstacles for CAD/CAM integration. In this work optimum cutting parameters, the best sequence, number, and type of passes of turning operation are determined by Genetic Algorithm (GA). Proposed optimization strategy ensures that no constraint will be violated at the optimum condition and determines the optimum number and type of passes such as rough, finish and semi-finish passes to complete a multipass turning operation. Here objective function is the unit production cost and constraints are limits of cutting force, power, tool life, stability condition, tool chip interface temperature, surface finish, feed rate to depth of cut ratio and the available rotational speed of spindle of machine tool.

Characteristics of Excimer Laser Ablation for Three Dimensional Machining of PMMA

In this research, machining characteristics of excimer laser ablation for three-dimensional machining of PMMA (Polymethyl methacrylate) is examined. In general, excimer laser ablation of polymeric material has features such as high precision and fine surface quality resulting from a less thermally-affected process, but in an earlier study, a thermal like effect on ablated surface was observed. Therefore, in this research the best machining condition of excimer laser ablation for PMMA by both numerical and experimental approaches was revealed.

Development of Flexible Worktable for Endmilling Based on Parallel Mechanism

Parallel mechanism has many advantages, such as high stiffness, high accuracy, high degree of freedom (DOF), etc. These fine features are suitable for work table of machine tools for production of recent complicated designs. In this study, six axes linear-actuated parallel mechanism was chosen as the basic design for work table. First, geometrical parameters of the table were designed to satisfy the required movable range with minimum cutting load. Then, the work table was actually constructed and its performance was evaluated. From positioning accuracy measurement, it was found that the table is suitable to be used for machining of complicated products. On the other hand, from actual cutting tests of primitive shapes using chemical wood and measurement of the machined shapes, potential of the table for real cutting application was confirmed.

High Efficiency Tool Path Generation for Freeform Surface Machining Based on NURBS Subdivision

Along with the rapid development of CAD/CAM system, the smooth surfaces are widely used in industry design. Especially NURBS surface attracts rising attentions because NURBS can describe flat surface, freeform surface and so on. Currently a lot of tool path generation patterns are proposed for milling process of freeform surface. Nevertheless there are still some problems on generating efficient tool path for freeform surface under the requested surface finish roughness. In this research, in order to resolve these problems, NURBS surface is divided into some patches and the tool path is generated on each patch. This paper proposes a surface divide method and makes a comparison between this method and undivided method. As a result, it is found that dividing the surface is helpful for the making shorter tool path and increase the machining efficiency.

Positioning Calibration of a Parallel Mechanism Worktable with 6-DOF

In this study, a small 6-DOF (degree of freedom) parallel mechanism worktable for machine tool was developed. There are many factors that affect the positioning precision and the accuracy of the machine tool. The uncertainty in position is mainly due to the structural rigidity, the geometric error of the parts and the assembly errors. It is very difficult to estimate the assembly errors and the link parameter of each part. Moreover, it is necessary to make clear the relation of cross talk between each axis for parallel mechanism. In this research, a method to compensate the movement error of worktable based on the measurement result was proposed and discussed. First, in order to measure the positioning accuracy of the worktable a measuring method by using 3-dimensional coordinate measuring machine (CMM) was proposed. After the evaluation, the positioning accuracy of the parallel mechanism worktable, the error of each configuration parameter can be obtained. By the correction of the inverse kinematic program, the improvement of the positioning accuracy of the worktable was confirmed. After calibrating several times, the positioning error became stable within a constant range. It is confirmed that this method to obtain the parameter error is effective, and it is possible to improve the positioning accuracy.

Robust Production Scheduling Using Autonomous Distributed Systems

This research proposes a method of production scheduling using autonomous distributed systems. A concrete message protocol is proposed to realize the production scheduling which includes not only Machine but also Human and AGV scheduling. Moreover this method realizes real time scheduling and parallel scheduling. Therefore, a new structure of production scheduling is proposed, which can realize a change of the type of production scheduler to correspond with a type of production system.

Measurement of Movement Error and its Compensation for 6-DOF Parallel Mechanism Worktable

In this study, a small, 6-DOF (degree of freedom) parallel mechanism worktable for machine tool was developed. There are a lot of factors that affect the positioning error and the accuracy of the machine tools. The uncertainty in position is mainly due to the rigidity of the structure, the geometric error of parts and assembly errors. It is very difficult to estimate the assembly errors and the link parameter of each part. In this paper, the uncertainty factor in positioning of the worktable was investigated and compensated based on measurement of movement error by using coordinate measuring machine (CMM).

Registration of 3-D Shape with Free-Form Surface Using Imageware and Genetic Algorithm

Registration of 3-D shape is significant in quantizing the error between the part and its CAD model and evaluating the parts manufacturing accuracy. In the past, various improved methods of the iterative closest point (ICP) had been proposed in registration. However, without fine initial pose of point clouds, the ICP algorithm often could not converge to the best (or near best) solution. According to the characteristics of 3-D shape with free-form surface, a new method for registration of 3-D shape with free-form surface is given, by which there are not rigid requests in initial pose of point data and the 3-D shape model could be in arbitrary positions and orientations in space. To improve the efficiency and accuracy of solving, this method is divided into general registration and fine registration. General registration is to fit rapidly and roughly the measured point cloud to designing point cloud from CAD model by Imageware. Fine registration is to further accurately fit the two group points using genetic algorithm (GA). Case study is finally given for a work piece with free-form surface to show the effectiveness of the above method.

Generating the measurement points based on finishing NC data

Inspecting the machined-product shape demands accurate measurement of a large number of measurement points, such that the actual shape may be fully characterised. Basically, the measurement points are generated manually by the operator by inspecting the machined-product model. However, for high variety low mass production, the generation of the measurement points needs to be done automatically to increase the measuring efficiency. This paper aims to develop a method that can automatically generate the measurement points for any 3D shape, machined by 3 axis milling machine, without the need to inspect the machined-product model. The generation of the measurement points is based on finishing NC data. The proposed method involves the following main steps: extracting the CL points from the NC data, sorting the extracted points and finally estimating the machined-product surface coordinates from the extracted and sorted CL points via projection process. The estimated machined-product surface coordinates are used as measurement points. Consequently some illustrative examples show the possibility that the method can be applied to various 3D shapes, machined by 3-axis milling machine.