In this paper, we propose a practical method for evaluating the robustness and stability of rotating machines. This entails using electromagnetic excitation and measuring the frequency response functions (FRFs) of the rotor system during rotation. The difficulty of applying excitation can be solved by utilizing a built-in motor with static eccentricity and adding a sinusoidal sweep d-axis current to the motor. A test rig with a bearingless motor (BELM) was used to verify the validity of the proposed method. A consequent-pole-type BELM is a combination of a consequent-pole-type motor and a radial magnetic bearing, in which both the motor and the suspension windings are arranged in one stator core of the BELM. The center of the motor is defined by the zero-power controller and the static eccentricity is determined by the suspension control system. The FRFs measured utilizing the electromagnetic excitation generated by the motor windings was compared with reference FRFs measured utilizing the suspension windings. The natural frequencies and damping ratios were determined from the two different FRFs. The difference between the identified natural frequencies and the difference between the damping ratios for the two different FRFs were calculated. The effectiveness of measuring the dynamic characteristics of the rotor system under various rotational conditions, such as the rotational speed and eccentricity, was clarified and the differences between the measurements obtained from the two different FRFs were generally less than 7.7%.
The optimal molecular design of organic friction modifier (OFM) additives allows for a reduction in the friction and wear in mechanical systems, and thus, an improvement in the energy efficiency and reduction in CO2 emissions. In this study, we synthesized N-(2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl)dodecaneamide, referred to as C12TEMPO, which has a large and rigid cyclic head group containing a free radical, to explore its application as a new type of OFM. We also selected stearic acid and stearonitrile, which possess small head groups without free radicals but an identical tail structure and approximately the same total length as C12TEMPO, to clarify the effect of head groups. The three types of OFMs were added separately into polyalphaolefin oil at 1 wt.%, and their lubrication performance was measured with a pin-on-disk type friction tester under varied normal loads or sliding speeds. C12TEMPO exhibited the highest load-carrying capacity, up to roughly thrice that of stearic acid and stearonitrile. Additionally, C12TEMPO gave rise to more stable sliding than stearic acid, as confirmed from comparison of instantaneous friction coefficients. These results suggested that C12TEMPO could form an effective boundary film that was robust to heavy-loaded sliding. The reason for this could be attributed to not only the strong surface interaction owing to the free radical but also to the rigidity of the cyclic structure of the head group in C12TEMPO. The results obtained when varying the sliding speed suggested that the efficiency to form the boundary film followed the order: stearic acid > C12TEMPO > stearonitrile. We inferred that the relatively large size of the head group of C12TEMPO rendered it difficult to access the solid surfaces, thereby reducing the film formation efficiency.
In this paper, the method of machining and correcting the two sides of tooth surface of spiral bevel gear pinion with the same cutter head and machine tool is studied. In this method, the cutting procedure and tool path are planned, and the calculation of motion parameters is completed. According to the characteristic that NC machine tool can adjust cutter location in real time, the tooth length and curvature are corrected, and the calculation model of tooth surface deviation is constructed. Five-cutter is used as the target tooth surface to optimize the cutting parameters. An example is introduced to carry out the analysis and gear cutting experiments, which verifies the feasibility of the proposed method.
Forging is one of the important manufacturing technologies to produce various mechanical components with high productivity. Recently, servo press that can control the back-pressure and the slide motion during the forging has attracted attention for high product quality without losing productivity. However, the back-pressure or the slide motion that affects the product quality and the productivity is completely determined by a trial-and-error method, and the determination is a crucial issue in forging using servo press. In this paper, a small product is selected as the case study, and both the back-pressure profile and the slide motion in cold forging are optimized. Numerical simulation using DEFORM3D is so intensive that sequential approximate optimization using radial basis function network is adopted to determine them. Based on the numerical result, the experiment using servo press (H1F200-2, Komatsu Industries, Corp.) is conducted. Through the numerical and experimental result, the validity of the proposed approach is examined.
In this paper, a novel geometric modeling method is proposed to construct generalized cubic developable C-Bézier (GCDC-Bézier, for short) surfaces with shape parameters. By using the control plane with generalized cubic C-Bézier basis function, the GCDC-Bézier surfaces are designed, and the shape of the surfaces are adjusted by changing its shape parameters. In addition, the necessary and sufficient conditions of G1 continuity and G2 Beta smooth continuity between two adjacent GCDC-Bézier surfaces are derived. Finally, we also discuss some properties of the GCDC-Bézier surfaces. The approach proposed in this paper provides a valuable alternative to the existing geometric modeling methods of developable surfaces.
The construction of free-form complex curves is very hot topic in engineering and computer aided design/computer aided manufacturing (CAD/CAM). The trigonometric Bézier-like curves got more attention in the fields of mathematics and engineering in recent years because of their useful geometric properties as compared to classical Bézier curves as well as ordinary Bernstein basis functions. The new trigonometric cubic Bézier-like (or TC Bézier-like, for short) curves along with new trigonometric cubic Bernstein-like (or TC Bernstein-like, for short) basis functions with single shape parameter with continuity conditions are presented in this paper. The necessary and sufficient constraints for C2 and G2 between two contiguous TC Bézier-like curves are constructed in order to remove the difficulty to composite curves which they cannot often be constructed by means of single curve. The role of shape parameter on connected curves with detailed smooth continuity steps is also part of this study. The ellipses and parabolas can also be represented exactly by using the TC Bézier-like curves. Some important applications of TC Bézier-like curves as: approximate some conic curves, font designing and free form complex curves are discussed. Some modelling examples show that the proposed TC Bézier-like curve technique is time saving, very effective and efficient which they can easily be modelled and give a powerful tool to design engineering complex curves.
A method is proposed to manufacture spiral bevel gear by duplex spread blade method based on 4-axis CNC milling machine. Firstly, the geometry parameters and machine-tool settings are comprehensively considered. To meet with the tooth taper, a new way is raised to select reference point. Then machine-tool settings are calculated that only first-order mesh performance is guaranteed in the reference point. Therefore conjugate tooth surface is modified by a surface represented as second-order polynomial to optimize mesh performance, as a result a target tooth surface is established, and according to the sensitivity matrix the machine-tool settings are corrected. Finally, the proposed method is illustrated by a numerical example to reveal it’s effective and feasible.
Large curvature surfaces are often milled by straight-line interpolation method. However the misuse of the cutting parameters may lead to checkerboard texture on the machined surface. In this paper, the effect of interpolating straight-line length and tool path on the checkerboard texture on the milled surface is studied. The checkerboard texture is measured and characterized in terms of surface micromorphology and profile shape. Influences of the interpolation line length and milling path on the appearance of the checkerboard texture are analyzed. The influences of feed per tooth and pick feed on the checkerboard texture are discussed. Results show that linear interpolation method is readily to cause formation of the checkerboard texture on the milled surface of a workpiece. With the increase of the length of the interpolation line the present of checkerboard texture on the milled surface becomes more obvious, and vice versa. The bright and dark bands of the checkerboard texture are always perpendicular to the curvature plane of the milled surface. The feed per tooth and pick feed may influence the appearance of checkerboard texture as well.
In Japan, most of the gear units for transmitting driving force in railway vehicles employ one-stage speed reducers. The gear unit is composed of a pinion connected to a traction motor via a coupling mechanism, a gear installed on an axle, and a gear case that covers them. In their rotating parts, tapered roller bearings are mainly used, and are lubricated by gear oil splashed by the rotating gear. In order to prevent seizure of the bearings and to improve the reliability of the gear units, it is important to appropriately adjust the bearing clearance. The bearing clearance can change from its initial value during the travel of the vehicles due to an atmospheric temperature and its initial value when assembling the gear unit, and can affect the performance of bearings. In this research, an actual gear unit was subjected to bench rotation tests under various bearing clearances and various atmospheric temperatures. The bearing temperature and torque were measured, and changes in bearing clearance were estimated. As a result, it is found that the bearing clearance decreases immediately after the rotation starts, and this tendency becomes more remarkable as the initial bearing clearance is smaller and as the atmospheric temperature is lower.
The motion accuracy of a precision reducer mainly depends on the transmission quality of the cycloid-pin gear, which is determined by the grinding accuracy of the cycloidal gear. The poor meshing characteristics caused by grinding errors in the cycloidal gear are the primary reasons for the low motion accuracy and short service life of a precision reducer. This paper proposes a quantitative correction method based on the grinding error of a cycloidal gear. This method allows the error in machine-tool grinding settings to be quickly and accurately corrected based on mathematical analysis and reverse engineering. A mathematical model of the grinding motion could be constructed based on the particularity of the continuous and closed profile of a cycloidal gear, and a cycloidal profile equation with the grinding settings as variables could be derived. A transitive equation for the grinding settings and tooth profile error was constructed using the closed reconstruction and optimal matching technology, and the essential relationship between the error extraction and quantitative correction was clarified. On this basis, a correction model was constructed, the correction strategy was planned, and the quantified correction of the grinding settings was realized using the numerical optimization method. Experimental results demonstrated that the quantitative correction method could quickly and accurately produce correction values for the machine-tool grinding settings. The tooth profile error could effectively be reduced with just one correction and two grinding operations. This study solved the technical problems that occur in the traditional machining process, which can only be corrected qualitatively and not quantitatively, and provided an effective way to improve the machining precision of the key parts of the precision reducer.
In order to improve a robust performance in a Multi-Input-Single-Output (MISO) control system, we proposed a loop-shaping methodology with the Robust Bode (RBode) plot for the MISO system. By using the current RBode plot, we are able to improve an existing Single-Input-Single-Output(SISO) control system with visualized guidelines on an open-loop characteristic Bode plot. Our proposed method transforms the robust performance problem for the MISO system into that for the SISO system in order to employ the RBode plot. As a result, we are able to design an improved MISO control system that compensates for disturbances against perturbations of controlled objects. A case study with the magnetic-head positioning control system shows that the proposed loop-shaping method is able to improve the positioning accuracy under the external vibration by about 83%.
In this study, the moving particle semi-implicit (MPS) method is employed for numerical simulation of flow field in gearbox of high-speed railway trains so as to understand the lubrication mechanism and mode in the gearbox during high-speed operation. A high-fidelity 3D model for a high-speed train gearbox under actual working conditions is created for the first time. RecurDyn and ParticleWorks co-simulation is conducted to acquire the flow field distribution in the gearbox under the coupling of multi-fields and to calculate the churning losses. Effects of key parameters including rotation speed, viscosity, and immersion depth on the churning power losses of the gearbox are investigated to determine their influences on the lubrication performance of the gearbox. Those results form a theoretical base for futuristic optimization of the high-speed train gearboxes.
While the price of electricity in Japan is increasing continuously, the plastic industry consumes considerable electric power for injection molding. The cost of electricity must be reduced to maintain product prices. Some strategies have been proposed to reduce the cost of electricity at the production stage, one of which is to reduce the contract electric energy amount with an electric company while increasing the facility operation rate and reducing excess power. This study proposes a method to minimize the electricity cost of injection molding lines by using the simulation for injection molding lines with an approximation solution. The simulated annealing method was used as the approximation solution. Based on the proposed method, numerous case studies were performed, and the results were analyzed.
Nowadays, 3 Dimensional (3D) Printing is an effective and fast way to fabricate prototypes. It can fabricate desired shape by layering multiple thin layers using various types of plastics. Making objects with 3D printing are faster and less expensive than the existed ways like machining, molding and etc. But 3D printed objects are not considered as high robustness because of making method of Fused Deposition Modeling (FDM) such as 3D printing. Following experiments are planned to compare the strength of 3D printed objects. In this research, Nylon 645 and blue, green, brown, blue colored Polylactic Acid (PLA) filaments are used to fabricate tensile and compression test specimens. First, specimens are tested to investigate a relationship between filament colors, extrude temperature and strength. Second, tensile test is conducted to investigate a relationship between the rate of infill and strength using PLA and Nylon 645 specimens. Third, compression test is conducted to investigate a relationship between the rate of infill and strength using PLA and Nylon 645 specimens. This research shows that extrude temperature does not affect strength and each colored PLA filaments have their own strengths. Brown colored PLA is strongest of the PLA filament in this experiment. Rate of infill affects strength significantly. As infill rate become higher, Ultimate Tensile Strength (UTS), Ultimate Compressive Strength (UCS), and Young’s modulus also become higher. The results of this research will help designing objects which be made with 3D print to be loaded.
Nowadays, robots have been utilized to perform a wide variety of tasks instead of humans, in which those equipped with hand-eye cameras have been proved to be useful in factories for handling metal parts. However, there have been difficulties for robots with vision sensors like cameras to detect a target objects’ 3D pose accurately, especially in the case that the target object is unique and the shape is arbitrary, and further, the object is moving. Visual servoing to moving target may enable the robot to pursue an animal to catch it. Aiming at achieving identification ability of a unique object, this paper utilized our previous study concerning photo-model-based object recognition. Based on the study, this paper applies the photo-model-based pose estimation method to video-rate stereo-vision position and orientation (pose) tracking, and it has been applied to an arbitrary-shaped moving target. To confirm the abilities of the proposed stereo-vision-based method to pursue an arbitrary target, real-time 3D pose estimation experiment to track the relative pose between a moving target and hand-eye robot have been conducted. The real-time experimental results show the proposed system can recognize the designated arbitrary-shaped target and track its pose in real-time.
This study explores a high reliability redundancy hydraulic power source, which includes shunt, throttle, relief, and switch modules that can continuously supply constant working pressure and steady flow in the case of input torsion and component failure. Considering the analysis of the working mechanism of each component of the energy control system, this study establishes the mathematical analysis theoretical model and selects the appropriate pressure and flow sensitive parameters, such as structure and spring. Through Amesim software, the physical simulation model is established, and the simulation research is conducted to analyze its static and dynamic characteristics. The redundancy fault tolerance capability of the system is also simulated and verified. Simulation results indicate that the output pressure and flow of the system can maintain stability with the fluctuation of input pressure. When the relief module fails in one branch, the output pressure of power energy remains unchanged, and the flow is halved. Although the maximum speed is attenuated, the system can still be guaranteed to run. The redundancy of energy system is realized, and the reliability of the system is greatly improved. The stable pressure and flow redundancy module designed in this study can keep the pressure and flow of the loop stable in the case of input pressure fluctuation. The system also has a good fault-tolerant function for all faults.
To enhance the cutting performance of chemical vapor deposit (CVD) diamond-coated tool, a short pulse laser grinding technique is applied. However, the thermal impact of a nanosecond laser damages the diamond crystallinity of the processed surface. To reduce this thermal impact, a femtosecond laser is innovatively used in this study to conduct the pulse laser grinding (PLG) of a CVD diamond-coated cutting tool, to achieve a sharpened tool edge with high quality. Furthermore, the CVD diamond tool edges processed by femtosecond and nanosecond lasers are compared based on sharpness, smoothness, and microstructure changes. The results show that a sufficient laser fluence higher than the threshold and a reduction in the pulse overlapping rate of the laser fluence of the femtosecond laser PLG could ensure a better tool edge shaping. A laser power of 7 W, processing angle of 20°, and scanning speed of 60 mm/s with roughness reduced to approximately half, are the suitable processing conditions of the femtosecond laser. From the observation of a scanning electron microscope, the tool edge processed by femtosecond laser PLG has a relatively sharp edge, with a radius of curvature around 1 μm, similar to that of a nanosecond laser. The further magnified images reveal a distinct processed surface characteristic. The nanosecond laser-processed surface has obvious longitudinal machining marks while that of the femtosecond laser has ablated debris. Moreover, the surface microstructure change of CVD diamond by femtosecond and nanosecond laser PLG are compared using Raman spectroscopy, further confirming that femtosecond laser could successfully suppress unfavorable structural effects in CVD diamond. Based on the results, femtosecond laser has a great potential for processing higher-quality CVD diamond tool edges.
Improving gear mesh efficiency contributes to reducing the environmental impact of vehicles. This study examined the effect of adjusting gear specifications on improving mesh efficiency. When the gear ratio of cylindrical gears is relatively high, it tends to increase the sliding velocity between the engaging gear teeth. Moving the contact region toward the base circle of the pinion along the line of action is considered to be one solution for reducing friction loss. However, it may cause deterioration of tooth surface strength because the radius of curvature of the tooth surface becomes smaller on account of being closer to the base circle. In order to confirm the influence of the gear meshing region on tooth surface strength, gear durability tests were carried out and tooth damage states were observed in detail under a microscope. The results revealed that pitting failure occurred near the tooth root region of the pinion. Furthermore, trochoidal interference due to the high torque condition extended over the base circle. In this case, trochoidal interference has a greater influence on pitting failure. In order to investigate the effect of reducing trochoidal interference near the base circle on pitting failure, further gear durability tests were conducted using the mating gears with large tooth tip modification. However, the effect on improving pitting durability was limited. Multidirectional, interacting wear was observed not only in the profile direction due to trochoidal interference but also in the lead direction due to edge contact. Such wear changed the location of pits. The results of these detailed investigation revealed a new viewpoint for explaining the mechanism of these phenomena in terms of conflict between pitting and multidirectional, interacting wear. Presumably, pitting failure changes if the state of progression of trochoidal interference and wear in the lead direction changes. In order to confirm the influence of such wear on pitting durability, a gear durability test was conducted using gears with tooth tip modification and endface relief. The test results confirmed that the location of pits and pitting durability changed. These results revealed that pitting durability and the state of damage were influenced sensitively and compositely by multidirectional, interacting wear, i.e., wear in the profile and lead directions.
A hitch mechanism with three rotational degrees of freedom(DOF) is proposed, which can be used on tractor in hill region. The three DOFs hitch mechanism is composed of two telescopic upper links, one lower link and one hanging frame of farm implements. The hitch mechanism can adjust the posture of farm implements and realize the profiling operation on hillside. It can improve the uniformity of the tillage depth during tilling on sloped land. We studied the inverse kinematics solution model of this hitch mechanism, which can be used to control the position and posture of farm implements. Furthermore, we carried out the mechanical analysis of the hitch mechanism and established the mechanical model, which can be used to calculate the lifting force parameters and power parameters of the driving element. The solution method of the important parameters is given in the given workspace of the three DOFs mechanism. Taking a 25kW hillside tractor as an example, under the condition of meeting the ISO tractor's standard, we calculated the length range of the upper link, load of the upper link and the lower link. The calculation results show that this mechanism is feasible for the Hillside tractor.
In this paper, a planar two-stage movable tooth reducer closed by input shaft is proposed. Through analyzing the motion transfer flow, the equation for calculating the speed ratio of the reducer is given. From the equation, the tooth numbers for realizing large speed ratio are determined. The power flow of the reducer is analyzed, and the equation of power flow calculation is given by which the conditions for generating closed power are determined. The output torque of the reducer and the force on the meshing pair are investigated, and the changes of the forces on the meshing pair with the parameters are analyzed. The three - dimensional design and motion simulation of the reducer are done which verifies the feasibility of the proposed reducer.
Better surface finish is believed to be one of the most important benefits of ultrasonic vibration-assisted milling. Many studies have shown that this benefit is most significant during slot-milling of a part when the vibration is applied in feed direction. To explicitly explain this phenomenon, an analytical model is proposed to predict surface roughness based on the trajectory of tool and the response of machined surface. The overall machined surface profile under tool trajectory depends on the tool tip movement, in addition to the tool deformation under cutting force and tool tip geometry. The movement of tool tip is governed by feed, spindle rotation, and ultrasonic vibration. The tool deformation depends on the milling force and stiffness. The geometry of tool tip is characterized by the tip radius and angle. Besides surface profile under tool trajectory, the response of machined surface is considered by assuming pure elastic deformation when the actual instantaneous cutting thickness is smaller than a critical value. In that case, part of the material is recovered so the actual machined surface profile is different from the profile under tool trajectory only. Surface roughness is then calculated based on the actual surface profile. Experiments are conducted on Aluminum alloy in both conventional and ultrasonic vibration-assisted milling under different spindle speed, feed, and vibration amplitude. Through the comparison between the analytical predictions and experimental measurements, the proposed model has high accuracy in all cases with average percentage error of 15%.
The original Iwan-type model is always based on the quasi-static assumption, which neglects the dynamic properties of the frictional interface. In this paper, A Iwan-type multi-contact model is established to study dynamic stick-slip and creep in mechanical frictional pair. The individual contacts in this model follow a rupturing-reforming law, which enable the model to describe the relation between the fluctuation of friction force and the behavior of individual contacts. Thermal effect influences the rupturing of individual contacts, a process that contributes to a considerable difference in the prediction of friction force. Creep is examined in two aspects, namely, time dependence of nominal static friction coefficient and fretting response. This model exhibits the logarithm dependence of static friction coefficient on stationary time, a result that the quasi-static Iwan-type model cannot describe. The fretting responses under different parameters are investigated. The proposed model can satisfactorily describe the manner the average rupture threshold of individual contacts influences the maximum friction force and maximum fretting displacement. The energy dissipations under different oscillatory displacements are also evaluated. The relationship between tangential stiffness and average contact rupture threshold is studied under Gaussian and power law distributions of contact rupture thresholds. The paper elucidates that by introducing a new rupturing-forming law of individual contacts, the Iwan-type model can better describe the dynamic properties of the frictional interface.