In the previous reports, it was clarified that waving amplitudes in linear motion ball guide (LMBG) systems can be suppressed by optimization of the crowning shape on end of carriage's raceways. Moreover, the evaluation algorithm of waving amplitude considered table deformation and the design method of table parameters based on a desired waving amplitude were developed. Mounting surface errors for LMBG significantly affect the motion accuracy of LMBG, however, this phenomenon has not been clarified yet. In this study, therefore, this issue is clarified analytically. At first, the analytical model of LMBG system is constructed; the model can set on the initial five-way errors for carriage and rail of LMBG: horizontal direction, vertical direction, roll angle, pitch angle and yaw angle. Then, load distribution theory analyses with various misalignment are carried out. The analyes results show that the only horizontal error significantly affects the waving amplitude; other four-way errors affect little. These results also suggest that the proposed analysis can evaluate necessary mounting surface accuracy to achieve a desired waving amplitude. Furthermore, it is clarified that the LMBG's rating life is affected by the additional load due to misalignment.
Object manipulation is one of the essential tasks for a home helper robot, especially in helping a disabled person to complete everyday tasks. For handling various objects in a category, accurate pose estimation of the target objects is required. Since the pose of an object is often ambiguous from an observation, it is important to select a good nextviewpoint to make a better pose estimation. This paper introduces a metric of the object pose ambiguity based on the entropy of the pose estimation result. By using the metric, a best next-viewpoint recommendation method is proposed for accurate category-level object pose estimation. Evaluation is performed with synthetic object images of objects in five categories. It shows the proposed methods is applicable to various kind of object categories.
Estimation of translation between consecutive frames, i.e., odometry, plays an important role in autonomous navigation. This paper presents an odometry estimation method using sparse LiDAR points and image feature points. In case of sparse LiDAR measurements, it is difficult to accurately estimate depth at image feature points. Image feature points with low-accuracy depth cause misconvergence in odometry optimization. To improve the robustness to the misconvergence, a new method with a Gaussian process that estimates not only the depth at image feature points but also the variance is proposed. By using this variance, it estimates the residual of image features in the world coordinate with depth, or in the image coordinate without depth. This allows more accurate and robust estimation than conventional methods in case of sparse LiDAR points. In an experiment with simulated sparse LiDAR points from the KITTI dataset, the proposed method is confirmed to estimate the odometry more accurately than conventional methods.
The purpose of this research is to elucidate the dynamic characteristics of linear motion ball guide (LMBG) and to propose effective analysis methods. First, we will explain how to apply translational and rotating vibration models to the load distribution theory, which is a static analysis method of LMBG. Next, we will introduce an example of analysis of time history response and frequency response using LMBG dynamic simulation. In order to verify the theory, we conducted an experiment to intentionally excite the vibration modes in three directions of vertical, rolling, and pitching, and compared the theoretical value and the measured value for the natural frequency of each mode. We also considered the effects of differences in the mass of the load and the preload amount of LMBG on the natural frequency of each mode. It was confirmed that the theoretical values obtained by the LMBG dynamic simulation showed the same tendency as the measured values, and were quantitatively almost the same.
Curved hole drilling method by electrical discharge machining (EDM) using suspended ball electrode composed of a metal ball and flexible thin foil has been developed, and it was clarified that curved and bending holes with various curving and bending angles into various workpiece materials could be machined by controlling the workpiece tilting angle during the process. However, the shape accuracy of the holes is not sufficient for practical applications. In order to improve the shape accuracy of bending holes, the bending hole EDM drilling technique using a foil supporting guide was proposed in this study. In EDM drilling into aluminum alloy and carbon steel, the drilling performance was very stable. Without using the foil supporting guide, the bending angle was larger than the designed one at the bending corner. By contrast, bending holes with various bending angles, such as 10 - 100°, could be accurately formed by using the foil supporting guide. Furthermore, practical hole shapes, such as Z-, U-, Y- and T-shapes were successfully formed by combining bending and straight holes.
This paper presents the application of a noncoated carbide drill having a sharp cutting edge and multistage point angle (drill A) for drilling carbon fiber reinforced thermoplastics (CFRTP). The cutting characteristics were evaluated by comparing the drill A with a diamond-coated carbide drill having a constant point angle (drill B). The influence of the contact state between the cutting edge and carbon fiber on the cutting force was evaluated using a CFRTP with a unidirectional fiber. The drill A exhibited a maximum thrust force at the drill rotation angle where the fiber orientation and cutting edge travel direction matched. It was found that the thrust force of the drill A was lower than that of the drill B at any drill rotation angle. Moreover, the thrust force of the drill A was always lower than that of the drill B during the drilling of the CFRTP with a plain-woven fabric. Additionally, the uncut fiber of the drilled hole obtained by the drill A was more satisfactory than that obtained by the drill B. The temperature of the area near the cutting point during the drilling was lower in the drill A than in the drill B. In the drill A, the thrust force tended to increase with the number of drilled holes. However, no considerable reduction in the drilled hole quality was observed at 200 holes.
When an NC machine tool is utilized during the machining process, acceleration/deceleration control is adapted for axes motions of the machine tool. Simultaneous acceleration/deceleration controls are applied to multiple axes to achieve smooth motion of the machine tool axes. However, such a technique does not accurately realize the designated motion speeds of the axes and cutting tool paths. In addition, the deflection of the cutting tool owing to the cutting force further increases machining error. Therefore, the actual tool paths must be identified and be corrected according to cutting-tool deflection to improve machining accuracy. The actual feed speed, which is controlled by the acceleration/deceleration of the cutting tool at each point on the tool path, must be identified to predict the cutting force precisely and estimate the tool deflection accurately. In this study, model equations were established to estimate the feed speed of the machine tool axes. The cutting force applied to an end-mill and a ball-end-mill could be precisely estimated using the estimated feed speed of the cutting tool. Then, the estimated cutting force was applied to predict the tool deflection accurately. Consequently, the tool paths were corrected based on the predicted tool deflection for high-accuracy machining. The effectiveness of this correction technique was verified through machining tests.