To improve the machining efficiency and reduce the overall manufacturing cost, a new model of machining hypoid gears by tilt cutting method is setup. Unlike the traditional cradle-style mechanical machines, the new model has no cradle and eccentric drum, the tool swivel drum is controlled by NC system. Firstly, according to its special structure, the mathematical model of the machine tool is built, an algorithm is developed to calculate the motional parameters. After building the machine tool model by the software Vericut, cutting simulation is performed. Based on the comparison of gouge and excess amount between simulated model and theoretical model, the tooth cutting experiment is conducted. Then, measurement and rolling detection for the hypoid gears is performed. The results indicate the rationality, reliability and accuracy of newly designed model of the milling machine. Moreover, the proposed method of calculating the motional parameters is feasible, which would be meaningful for future industrial application.
The mechanism of failure of heat exchanger and steam generator tube-to-tubesheet joints is related to the level of residual stresses produced in the tube expansion and transition zones during the expansion process and their variation during operation. The accurate prediction of these stresses based on the plastic and creep properties of the joint materials involved can help to design for better leak tightness and strength. Existing design calculations are based on an elastic perfectly plastic behavior of the expansion joint materials and do not account for creep. The proposed model is based on a linear strain hardening material behavior and considers the joint contact pressure relaxation with time. The interaction of the tube and the tubesheet is simulated during the process of the application of the expansion pressure and operation. The effects of the gap, material strain hardening and creep properties are to be emphasized. The developed model results are validated and confronted against the more accurate numerical FEA models.
In this paper, a delivery workload balancing problem in an assembly plant is considered. The problem is first described as a special case of the unrelated parallel machine scheduling problem of minimizing the makespan. Then, a polynomial time heuristic algorithm is proposed, which is regarded as a dynamic programming procedure to compute a linear partition of a specified list of given jobs. In addition, a simple improvement procedure based on local search technique is discussed. Numerical results indicate that from the viewpoints of solution quality and execution time both, the proposed heuristic is applicable in the practical situation.
This study investigates the robust topology optimization of a thin plate structure under a concentrated load with load position uncertainty. The effect of uncertain load direction, load magnitude, and load distribution in topology optimization problems has been investigated in previous research, but few studies have dealt with robust topology optimization considering load position uncertainty. In this study, load position uncertainty is modeled using the convex hull model, in which the load position uncertainty is confined within a circular area whose center is at the nominal load position. The worst load condition is defined as that when the applied load is at a position in the convex hull that gives the worst value of the mean compliance. Here, the robust objective function is formulated as a weighted sum of the mean compliance obtained from the mean load condition and the worst compliance obtained from the worst load condition, with a plate model based on Reissner-Mindlin plate theory. The robust topology optimization problem is formulated using a level set-based topology optimization method. Through numerical examples, robust optimum configurations are compared with deterministic optimum configurations and the validity of the proposed robust design method is then discussed.
A control chart is an important tool of the statistical process control for monitoring deviations from a stable production process. For this purpose different control schemes have been developed for the fast detection of certain changes in the process parameters. We reconsider the recently proposed exponentially weighted moving average (EWMA) chart based on the mean absolute deviation from the median (called EWMA-MD chart) to monitor the process variation. The repetitive group sampling scheme through two pairs of control limits has been incorporated in the proposed control chart to enhance the performance. The performance of the proposed control chart is evaluated in terms of the average run length through simulation when the quality characteristic of interest follows a normal distribution, a gamma distribution or a t-distribution. The results show better detecting ability of the proposed control chart as compared with the existing EWMA-MD chart for small to moderate shifts in the process dispersion.
We developed a new method that can diagnose damage on a gear tooth surface using a laser beam without a rotary encoder. The method procedure is as follows: 1) The tooth bottom, the tooth tip and their two median values are detected using the differential values of the laser reflection data. 2) The gear rotation speed is calculated with these four positions, and interpolated according to the rotation fluctuation. 3) Using the calculated gear rotation speed, the measured data can be converted to the corresponding gear rotation angles. Thus we can diagnose the damage of the gear tooth surface precisely and can easily set up the experimental measurements without being influenced by rotational fluctuation. To confirm the validity of the method, we conducted the diagnosis experiment and we created contour maps to show the diagnosis accuracy variation according to the fluctuations of the amplitude and cycle. Based on these maps, we found that the diagnosis accuracy of the damage size is the same irrespective of the presence or absence of a rotary encoder. The diagnosis accuracy of the damage location without using a rotary encoder is lower than the result obtained using a rotary encoder because we assumed that the detection of the damage start point is delayed using this new method. Furthermore, we defined the limit using the conditions of this method from the sampling theorem; the validity of this definition could also be confirmed from the contour map.
Aiming at efficient locomotion on the ground and safe stairs climbing for aged or physical disabled people, a wheel-track hybrid electric powered wheelchair (EPW) is designed, analyzed, and demonstrated extensively on various conditions. We first present the wheel-track hybrid design of the EPW with a focus on the mechanical structure and of onboard control system. We then discuss and analyze the wheel and the track mobile modes and their switching design of the EPW. The use of the track mobile mode is primarily for climbing up and down the stairs while the wheel mobile mode is for commonly ground surfaces. The mechanics analysis during these two mode switching and in the process of climbing up and down the stairs are also presented in the paper. The simulation and experimental results show that the new wheel-track hybrid EPW can effectively conduct the two locomotion modes including climbing up and down the stairs. The results also validate the motion mechanics calculation models and the dynamic mode switching between two mobile modes.
In the sampled-data positioning control system of mechatronic products, it is hard to analyze the effect of mechanical resonances above the Nyquist frequency after the control systems were assembled. However, unexpected variations of mechanical characteristics often happen in actual mechatronic systems. To solve such a problem, this paper proposed two analysis methods with measurable open-loop characteristics in single-input/single-output (SISO) sampled-data positioning control systems. These methods use frequency responses of the controlled object and the digital controller for calculating the measurable open-loop characteristics without complicated calculations involving state-space representations of a controlled object, or integrations of matrix exponentials. The proposed methods indicate that we can analyze the performance of the sampled-data control system beyond the Nyquist frequency by using these measurable open-loop characteristics. To show the validity of the proposed methods, this study conducted simulation analyses on the sampled-data positioning control system of a magnetic head-positioning control system in a hard disk drive. These results show that proposed open-loop characteristics are good approximated solutions in order to analyze the control system performance of the sampled-data positioning control system beyond the Nyquist frequency.
Lunar/planetary spacecraft should be able to land softly and conduct thorough explorations. Conventional landing methods suffer from various problems such as high rebound, the impossibility of reuse, and necessity of air. Therefore, a novel landing method that solves these problems is required for landing in severe environments. Toward this end, the authors have applied Momentum Exchange Impact Damper (MEID). MEID realizes landing by exchanging the momentum of the spacecraft with damper masses. However, flying damper masses may collide with and damage the spacecraft. Furthermore, they may pollute the lunar/planetary surface. Therefore, in this paper, the authors propose a Non-Flying-Type MEID (NFMEID) mechanism without flying damper masses. Unlike conventional landing methods and MEIDs, the NFMEID (i) reduces a spacecraft's rebound, (ii) can be reused, (iii) can be used in vacuum, and (iv) can protect a spacecraft and the surface pollution from launched masses. Furthermore, the NFMEID may extend the usefulness of MEID because it is considered effective for the shock response control of not only spacecraft but also general mechanical structures. This paper explains the NFMEID mechanism and evaluates its landing performance through some simulations. This study shows that the NFMEID is a promising landing method for further lunar/planetary exploration missions.
The vibration and noise from internal gears is an important issue in mechanical devices such as automobiles. The characteristics of the vibration and noise of internal gears are markedly influenced by micrometer-order manufacturing errors of the tooth flank form. Therefore, quality control using a measuring instrument is required. The accuracy of a gear measuring instrument is usually evaluated using a master gear. However, it is difficult to manufacture master gears with high accuracy because the reference surface of a master gear for an internal gear has a geometrically complicated form. This limits the accuracy of the evaluation and calibration of measuring instruments for internal gears. In order to address this problem, the present paper proposes a novel artifact with a concave spherical surface for the evaluation of the accuracy of measuring instruments for internal gears. A concave spherical surface can be manufactured with high accuracy because of its simple features. As such, a highly accurate artifact can be developed using this surface. In the present paper, the concept for the proposed artifact is described, and a mathematical model for the measurement conditions of the artifact is constructed. The design of the artifact is described, and an evaluation method for the measuring instrument is developed. The artifact is then manufactured, and its accuracy is calibrated. A measurement experiment using the proposed artifact is carried out, and the effectiveness of the evaluation method is verified.
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