Search

This study investigated the effects of simultaneously machining pilot holes and threads, as well as the accuracy of thread machining after pilot hole drilling. In addition, the thread machining of S50C and SKD61, which are work materials with different hardness, was also examined. Furthermore, a smart machining method for thread milling using helical interpolation was developed by monitoring cutting data using a wireless holder. The results show that the proposed monitoring method is effective for improving the accuracy of thread machining using helical interpolation motion of the threading tool. Moreover, this study discussed the differences in results due to the presence or absence of pilot holes. Finally, the influence of the hardness of the work material on the results was analyzed. [ABSTRACT FROM AUTHOR]

A five-axis machining center (5MC) is capable of synchronous control, which makes it a feasible tool for quickly and accurately machining complicated three-dimensional surfaces, such as propellers and hypoid gears. Recently, the necessity of improving both the machined shape accuracy and the machined surface roughness of free-form surfaces is growing. Therefore, in our previous study, we aimed to maintain the feed speed vector at the end-milling point by controlling two linear axes and a rotary axis of the 5MC to improve the quality of the machined surface. Additionally, we developed a method for maintaining the feed speed vector at the end-milling point by controlling the three axes of the 5MC to reduce the shape error of the machined workpieces (referred to as the shape error herein), considering the approach path of the tool determined via calculation. However, a high machining force at the start of the workpiece cutting was observed and the factor contributing to this phenomenon was not determined, although this phenomenon leads to a shape error to a certain degree according to the machining condition. In this study, the main objective is to suggest a method to reduce the machining force at the start of the workpiece cutting and shape error. Hence, we develop a theoretical method to estimate the machining force by using an instantaneous cutting force model, which considers the synchronized motion of two linear axes and a rotary axis of the 5MC. Subsequently, we determine the most suitable approach path of the tool considering the prediction of the machining force. The results of this study indicate that the machining force can be estimated by applying an instantaneous cutting force using the feed per tooth and machining angle, and that both a high machining force at the start of the workpiece cutting and shape error reduction can be realized by using the proposed approach path of the tool. [ABSTRACT FROM AUTHOR]

In this study, an existing superfinishing method used for polishing glass surfaces was refined using a five-joint closed-link compact robot with fixed abrasive grains. In previous studies, a voice coil motor was used to control the constant-pressure pressing force while maintaining the polishing force for a relatively short period. However, maintaining the polishing force for long periods is imperative for achieving a high-quality polished surface. Thus, in this study, a strain gauge load cell was adopted in addition to a conventional piezoelectric force sensor to maintain the polishing force for a long period. First, the amounts of DC drift of the piezoelectric force sensor and strain gauge type load cell were compared to confirm the necessity of signal processing as well as the compatibility of long-term force measurement and high-frequency vibration measurement by application. Further, a method was proposed in which the change in the pressing force was recorded from the connected sensor; when the pressing force fluctuated, chatter vibrations were determined to occur, and the pressing force was temporarily set to 0 N. This method could obtain a better polished surface than the proportional-integral-differential (PID) control, which simply controls the pressing force at a constant value. Finally, chatter vibrations could be determined by detecting high-frequency sounds using a sound level meter. Notably, a finely polished surface could be obtained. [ABSTRACT FROM AUTHOR]

In recent years, collaborative robots able to work together with humans have become widespread in production sites and factory automation fields. In this context, the goal is to provide a production site where cooperative robots can share various types of tools with humans. However, we have not yet reached the point where collaborative robots and humans can share tools for advanced skills. Therefore, it is very important to investigate how a collaborative robot can control advanced tools requiring human skills and the processes for realizing such control. Musical instruments are some of the most difficult tools to handle. It is important to focus on musical instruments because they allow us to evaluate the robot's manipulation not only by evaluating its movements, but also by evaluating the resultant sound. In this study, we consider a flexible and large deformable musical saw as an unknown and advanced tool difficult for humans to manipulate. In a previous report, a support method for imitating a human was adopted and provided manipulation control based on striking sound feedback using a cooperative humanoid robot. In the present paper, the support method is improved at the tip of the musical saw to realize an advanced wrist motion. In addition, we discuss skillful manipulations based on striking sound feedback control while considering the positions and postures between the collaborative humanoid robot and musical saw. [ABSTRACT FROM AUTHOR]

Using computational fluid dynamics (CFD) technology, a stable manufacturing method for polymeric nanofiber non-woven fabrics based on an improved melt-blowing method and flash spinning is realized to achieve mass productivity. Subsequently, a method to predict filter efficiency using two production methods based on the effects of thickness, filling rate, and fiber diameter on filtration performance is developed to establish a filter design via CFD technology. CFD models featuring uniform fiber diameters are proposed. Next, the pressure loss and flow resistivity are calculated using CFD flow analysis software, as in a filter experiment. The proposed fiber diameter distribution model yields results similar to the experimental value, and the relationship among filling rate, fiber diameter, and flow resistivity is verified. The non-woven filter fabricated in this study demonstrates superior filtration properties, based on the results. Additionally, a method to satisfy both low pressure loss (low flow resistivity) and high filtration efficiency is discussed. Although the pressure loss increases, the filter yields a value below the standard for high-performance face masks, since the fiber diameter is on the nano-order. [ABSTRACT FROM AUTHOR]

A five-axis machining center is known for its synchronous control capability, allowing complicated three-dimensional surfaces, such as propellers and hypoid gears, to be quickly created. Prior research has shown that it is necessary to improve not only the machined shape accuracy but also the machined surface roughness of free-form surfaces. Therefore, in this research, we aimed to maintain the feed speed vector at the endmilling point by controlling two linear axes and a rotary axis with a five-axis machining center to improve the machined surface quality. In previous research, we suggested reducing the shape error of machined workpieces (referred to as shape error in this research) by considering the differences in the servo characteristics of the three axes in the machining method. The shape error was significantly decreased by applying the proposed method, which uses a parameter (referred to as precedent control coefficient in this research) determined by calculation, rather than trial and error. Moreover, to maintain the feed speed vector at the endmilling point when machining complex shapes, a rapid velocity change in each axis is required, causing inaccuracy owing to torque saturation. The results of the experiments and simulations of previous research indicated that torque saturation can be evaluated via simulation. In this research, to reduce the shape error while avoiding torque saturation when movement has high angular velocity, we developed a theoretical method to obtain the most suitable precedent control coefficient of each axis by using a block diagram that considers torque saturation. Therefore, both shape error reduction and torque saturation avoidance can be realized by using the proposed method. [ABSTRACT FROM AUTHOR]

Planetary gear trains (PGTs) are widely used in many machines and are one of the most important mechanisms in hybrid and electric vehicles. Previous research, based on empirical knowledge gained from the automobile industry, indicates that high carrier-support stiffness and low ring-gear support stiffness are required to reduce ring-gear errors. Therefore, here, we evaluate the vibration characteristics of a PGT as a function of the support stiffness, which is varied by inserting urethane rubber into the driving shaft. We conducted experiments using a 2K-HV-type tester, which contains a coaxially rotating and revolving planet gear shaft based on a universal joint. This mechanism allows the observation of the inner workings of the mechanism with the use of a transparent acrylic carrier. We were able to detect the so-called "bounce" phenomenon consisting of a swaying motion when the rotation of the ring gear is reversed, and this result was confirmed by our internal observations of the mechanism. It is evident that the index of vibration increases due to the bounce phenomenon because the reversal of the ring gear causes a larger vibration than that of the carrier because the ring gear can vibrate without restraint, unlike the planet gear that is sandwiched between the sun and ring gears. Furthermore, the influence of the radial support stiffness of the driving shaft, load torque to the output shaft, and acceleration time of the reversing gear on the "bounce" phenomenon were evaluated. We found that a larger load torque corresponds to a greater difference depending on the acceleration conditions of the sun gear. During reversal, at the moment when the rotation speed is zero and rotation recommences, the ring gear exerts the maximum force, and the larger is the load torque, the greater is the effect of the difference in acceleration. [ABSTRACT FROM AUTHOR]

Because most industrial robots are taught using the direct teaching and playback method, they are unsuitable for variable production systems. Alternatively, the offline teaching method has limited applications because of the low accuracy of the position and posture of the end-effector. Therefore, many studies have been conducted to calibrate the position and posture. Positioning errors of robots can be divided into kinematic and non-kinematic errors. In some studies, kinematic errors are calibrated by kinematic models, and non-kinematic errors are calibrated by neural networks. However, the factor of the positioning errors has not been identified because the neural network is a black box. In another machine learning method, a random forest is constructed from decision trees, and its structure can be visualized. Therefore, we used a random forest method to construct a calibration model for the positioning errors and to identify the positioning error factors. The proposed calibration method is based on a simulation of many candidate points centered on the target point. A large industrial robot was used, and the 3D coordinates of the end-effector were obtained using a laser tracker. The model predicted the positioning error from end-effector coordinates, joint angles, and joint torques using the random forest method. As a result, the positioning error was predicted with a high accuracy. The random forest analysis showed that joint 2 was the primary factor of the X- and Z-axis errors. This suggests that the air cylinder used as an auxiliary to the servo motor of joint 2, which is unique to large industrial robots, is the error factor. With the proposed calibration, the positioning error norm was reduced at all points. [ABSTRACT FROM AUTHOR]

Monitoring technologies have attracted attention in the factory automation fields that rely on the Internet of Things (IoT). However, it is difficult to monitor the process information from a round machining tool during rotating operations. Therefore, we developed a novel tool holder equipped with a wireless communication function to monitor tool vibrations. In the present study, we attempt to measure the tool holder vibrations during ball nose end milling processes using the servo driving information for different machine tools. We demonstrate that, using the developed tool holder with a wireless system, it is feasible to improve the machined free form surface by considering the servo driving information. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the motion accuracy of a large industrial robot and its compensation method and constructed an off-line teaching operation based on three-dimensional computer aided design data. In this experiment, we used a laser tracker to measure the coordinates of the end effector of the robot. Simultaneously, the end-effector coordinates, each joint angle, the maximum current of the motors attached to each joint, and rotation speed of each joint were measured. This servo information was converted into image data as visible information. For each robot movement path, an image was created; the horizontal axis represented the movement time of the robot and the vertical axis represented the servo information. A convolutional neural network (CNN), a type of deep learning, was used to predict the positioning error with high accuracy. Subsequently, to identify the features of the positioning error, the image was divided into several analysis areas, one of which was filled with various colors and analyzed by the CNN. If the prediction accuracy of the CNN decreased, then the analysis area would be identified as a feature. Thus, the features of the Y-axis positioning error were observed for teaching each joint angle in the opposite direction just after the start of the motion, overshoot of the rotational joint current, and the change in the swivel joint current. [ABSTRACT FROM AUTHOR]

Recently, carbon fiber reinforced plastics (CFRP) have been used in various applications such as airplanes and automobiles. In CFRP molding, there are unnecessary portions on the outer area. Therefore, a machining process is required to remove them. Cutting and grinding are conventionally used in the finish machining of CFRPs. End-milling allows the removal of most of these portions. However, uncut fibers easily occur during end-milling. In contrast, a precise machined surface and edge are easily obtained using a grinding tool. Therefore, this research has developed a novel cubic boron nitride (cBN) electroplated end-mill that combines an end-mill and a grinding tool. This is a versatile tool that can cut and grind CFRPs by changing the direction of rotation of the tool. In this study, the effectiveness of the developed tool is investigated. First, the developed tool machined the CFRP by side milling. Consequently, cBN abrasives that were fixed on the outer surface of the developed tool did not detach in certain cutting conditions. Next, in order to generate a sharp edge on the CFRP and restrict the increase in the CFRP temperature with the cBN electroplated end-mill, the optimum abrasive size and grinding condition were investigated through the design of experiments. Moreover, the effectiveness of the developed tool was verified by comparing it with a conventional tool. As a result, smaller burrs and uncut fibers were observed after final machining with the developed tool under the derived optimum condition than those with conventional tools. However, the desired surface roughness could not be achieved as required by the airline industry. Therefore, oscillating grinding was applied. In addition, the formula of the theoretical surface roughness while using the developed tool was derived using the theory of slant grinding. As a result, the oscillating condition that led to the required surface roughness was obtained by theoretical analysis. In addition, the required value for the airline industry was achieved by oscillating grinding. [ABSTRACT FROM AUTHOR]

Currently, the demand for carbon fiber reinforced plastic (CFRP) has increased in various fields. However, there have been few studies investigating the machined surface quality, degradation in CFRP mechanical properties with machining temperature, or machining tool cost. In particular, the machining temperature is considered to affect the machined quality because the CFRP matrix is a resin. In this study, a cubic boron nitride (cBN) electroplated end mill was developed; this novel tool can switch between cutting and grinding without needing to change the tool. To observe the relationship between the amount of abrasive grain in contact with the CFRP and the occurrence of burrs, a grinding test was conducted with different clearance angles of the end mill and different abrasive grain sizes. The temperature during the grinding processes was measured, and the burrs were estimated after the grinding processes. From these results, the contact amount of the abrasive grit suitable for grinding was derived. [ABSTRACT FROM AUTHOR]

This research proposes a method to achieve laser quenching and laser forming simultaneously. This technique uses a diode laser to produce thin steel sheet-assuming parts, such as springs and hinges. Energy and time are saved by combining the advantages of laser quenching, which has high input heat efficiency, and laser forming, which, unlike press molding, does not require metal molds. In this study, laser-quenching molding was performed for an entire thin steel plate, and the influence on warping was investigated. Furthermore, the proposed method was evaluated under repeated quenchings for different cross-sections of a workpiece. The results indicated that the technique prevented bending deformation during the next laser scan and reduced warping by increasing the second moment of area of the entire workpiece. [ABSTRACT FROM AUTHOR]

In this study, the authors investigate improving the precision of a thread by deriving its radial force (thrust force) with a four-component piezoelectric dynamometer and thread cutting by helical interpolation motion using a thread mill. The accuracy of the thread is discussed with respect to changing hardness of the work material. In addition, by recording the position information at the time of thread cutting from the servo guide on the data logger, the relationships among the cutting forces of the four components and the radial force are confirmed by various methods; further, the consistency of these relationships was confirmed. [ABSTRACT FROM AUTHOR]

Nanofibers of polypropylene were produced by a modified melt-blowing method. The manufacturing method and thermal characteristics of fabricated nonwoven-fabric nanofibers were studied. Apparent thermal conductivity was measured as an evaluation of adiabatic properties, and a prediction model was developed with computational fluid dynamics (CFD) based on a one-dimensional computer-aided engineering method. In addition, we attempted to evaluate true thermal conductivity in consideration of lateral heat dissipation during measurement by thickness. Consequently, we determined the influence of the fiber diameter and thickness of the nonwoven fabric on the thermal conductivity and demonstrated that the proposed CFD model was effective for estimating the characteristics of the thermal conductivity of the nonwoven fabric. [ABSTRACT FROM AUTHOR]

Plastic gears are light and can be used without any lubricant, but they have low strength and an adverse effect on the environment. Therefore, a new gear that maintains these advantages while mitigating the disadvantages has been proposed. The development of sustainable and reproducible natural materials is desired to address these environmental problems. Therefore, in this study, a method was devised to extract high-quality and precise bamboo fibers using a machining center. Then, the hot press method was used to produce a novel spur gear made from only bamboo fibers, which is a green and organic machine element with a complicated shape. The present paper describes the characteristics of the proposed bamboo fiber gears, considering experimental results, including the hot press molding conditions, and the influence of fiber length on tooth bending strength, root strain, and vibration due to meshing teeth. [ABSTRACT FROM AUTHOR]