In the present paper, the job shop scheduling problem with no intermediate buffers, i.e. the blocking job shop scheduling problem, is investigated. Since there are no buffers between operating machines, the machines are blocked by the products that the machines operated until those products are passed to the products’ downstream machines. Under the condition where blocking is considered, complicated calculations must be performed to evaluate semi-active schedules when a partial change of a schedule, or exchange of an operation order of jobs on a specific machine, is planned. Furthermore, because some or most of the partial changes result in infeasible schedules, it will be an advantage to know the feasibility of the changes before the time adjustments for the semiactive schedule. To deal with the feasibility problem, a new optimization problem using an artificial variable is proposed for the feasibility evaluation of a partial change of a schedule. The proposed method utilizes the mixed integer programming problem of the blocking job shop scheduling problem, with the integer variables given so that the problem becomes a simple linear programming problem solved by the simplex method. By using the information before the change of the schedule, namely the basic variables and the deformed constraints, the optimization is performed efficiently beginning at a close solution of the present evaluation. Moreover, the semi-active schedules are determined within a few steps after the evaluation, which eliminates the calculation of determining the schedule separately. To demonstrate the behavior of the proposed method, examples of calculation procedures are described in a precise manner. In addition, numerical examples are shown to verify the advantages of the proposed evaluation method.
This paper presents a multi-dimensional loading material testing machine based on a hexapod parallel mechanism. We designed a model-based PID closed-loop control method using feedbacks from six uniaxial force sensors installed on limbs. Three simulations were proceeded to estimate the feasibility of this control method. Furthermore, we established two series of experiments, including multi-dimensional loading experiments and standard tension tests. The former experiment results demonstrate the multi-axial loading capacity since the actual multi-axial output wrench has the deviation less than 5% of the desired ones. The latter experiments reveal that the uniaxial tension test is not considerably influenced by the redundant degree of freedoms, because the tensile-test results are relatively identical to those results achieved by universal material testing machine. Both experimental results suggest that this proposed material testing machine are feasible to perform multi-dimensional material tests, as well as standard uniaxial tests.
According to the requirements on operating and controlling interventional catheter, a new design scheme for interventional catheter with a cable-driven active catheter system was proposed. A kinematics and dynamics model based on screw theory was achieved for special configuration on active catheter. Further, the control model of cable length was constructed through the relationship between driving cable length and motion state of the system. Thereby, the variation of the cable length in the planning task using this model was analyzed, which was verified by experiment. In view of the complexity of the system, dynamic characteristics using Kane's equation based on screw theory is analyzed in this paper. The needed driving torques of every joint are calculated in the environment of Mathematica when active head-end system is moving along planned trajectory, which provides theoretical basis for design and control of the system.
Chatter is one of the main limitations to milling performances. Prediction of such unstable phenomenon via stability lobe diagrams requires the measurement of the Frequency Response Functions (FRFs) for each tool and machine tool setup. This paper presents a hybrid FE-experimental approach to identify tool-tip FRFs with only one set of measurements, taking into account tool change without any other experimental test. Machine tool dynamics is modeled using a Finite Element (FE) approach. Machine, spindle and tool-holder are described by a lumped model characterized by frequency-dependent stiffness, while the tool is FE modeled. Lumped model and tool are connected by means of stiffness matrices extracted using the Craig-Bampton dynamic reduction method. The obtained simplified model of machine tool enables chatter prediction by means of stability lobe diagram for different tool without the need for extensive experimentation. Once a new tool is clamped no other measurements are needed, just the new tool FE model. Experimental validation under different conditions is provided, showing accuracy and reliability of proposed approach.
Ductile grinding of brittle materials has been demonstrated in achieving desired machining quality without deteriorating surface and subsurface quality and any post processing work. However, it is still in a low efficiency in micro-machining or conventional grinding. In this paper, a high speed diamond grinder was exploited to explore ductile grinding of SiC at a relatively higher material removal. A combination of ground surface, subsurface and grinding chips SEM observations are given to explain the high speed grinding mechanism for SiC. This study indicates that ductile grinding of SiC can be achieved through a combination of the increase of the wheel speed and the control of grinding depth. Moreover, the critical chip thickness for ductile grinding of SiC can be greatly improved under a higher grinding speed comparing to conventional speed grinding. Correspondingly, the material removal volumes can be substantially enhanced in high speed grinding while not affecting subsurface and surface integrity.
In face-to-face conversation, embodied rhythms between speech and body movements such as nodding are mutually synchronized between talkers such as a speaker and a listener. This synchrony is called entrainment in communication and it generates the sharing of embodiment in human interaction. Embodied communication, which is closely related to behavioral and physiological entrainment, is an essential form of communication that forms the basis of interaction between talkers through mutual embodiment. In particular, nodding has an important role as a regulator in embodied interaction and communication. The detection of nodding is useful for an estimation of the activity of conversation. In this paper, we develop a nodding detection system using a nodding detection model based on an analysis of the head movement involved in nodding. This model detects nodding based on the rotational movement of the head, which is estimated from the face tracking of the Active Appearance Model. The effectiveness of the system is demonstrated by comparing the result of the nodding detection results with visual inspection. The developed nodding detection system is demonstrated in an actual event for children.
Machining centers have been widely used for metal mold manufacturing processes because high-speed machining using small-diameter end-mills has become practical. However, because the concave portions of the metal molds used for injection molding are very complex and exacting, and also present large differences in depth, long, small-diameter end-mills have to be used for the metal mold manufacturing process. Unfortunately, such end-mills degrade the machining accuracy of the metal mold, because the cutting forces cause the cutting point to deflect considerably. The goal of this study was to improve the real-time compensation for machining errors caused by the deflection of small-diameter end-mills, such as ball end-mills. To achieve this goal, a system of compensating for the machining errors was proposed by using the estimation method obtained from preliminary experiments, and the system validity was verified by performing cutting tests. Cutting tests, in which the axial depth of a cut increased linearly with the cutting duration, were conducted for measuring the cutting forces during the end-milling. As a result, the proposed compensation system could be used for real-time estimation and correction of the machining error caused by end-mill deflection induced by the cutting force. Furthermore, we were able to reduce the machining error by 80% in both down and up cuts, while increasing the axial depth of cuts, by using the proposed compensation system.
In this study we give a feedback control method for steering support system. In this method we consider the stability of the path tracking control system under the limitation of steering angle, so that drivers can drive safer and more comfortable. In order to do this, we have derived linearized system from the nonholonomic kinematic system by the differential flatness consideration and linear control law which stabilizes the path tracking control system. Furthermore, feedback gains are tuned to satisfy the closed loop stability and the limitation of the steering angle by using Particle Swarm Optimization. Usefulness of the proposed control method has been demonstrated by experiments using a 1/10 scale robot car.
Torsional stiffness of a rotary feed drive system not only has great influence on the rotary positioning accuracy, but also affects the system dynamic characteristics. This paper proposes an estimating approach for the torsional stiffness of typical transmission chains in rotary feed drive tables. Firstly, a general analytical torsional stiffness model is presented, taking torsional stiffness of shafts and meshing stiffness between gear teeth into account. Then, general expressions of coefficients in the model relating adjacent angular displacements in the typical transmission chains are derived under static equilibrium condition. Moreover, a torsional stiffness test experiment is conducted for a rotary drive table and the stiffness estimation algorithm is presented. To verify the validity of the proposed approach, comparisons among the traditional model, finite element model and the proposed one are made. The results show that the stiffness value obtained from traditional model is bigger than the presented analytical model. The finite element analysis and experimental results indicate the analytical model is valid and more accurate than the traditional ones. This work provides an effective and general way to estimate the torsional stiffness of typical transmissions employed in rotary table of machine tools during the system design and characteristic analysis process.
The sideslip angle is used to control a vehicle for safety, however, it is hard to estimate the sideslip angle. In many researches, the estimator needs many unattainable variables, such as yaw inertia or cornering stiffness, to estimate the sideslip angle. This paper proposes the observer uses geometrically derived equations. The estimator needs a compensation value to estimate the sideslip angle instead of unattainable variables. The compensation value compensates the error from the imperfections of the formulas and nonlinearity motion at high speed. Estimator tunes its compensation value automatically, and uses the least squares method for estimating the compensation value and to apply to a real vehicle. Estimator is developed by LabVIEW, and gets the simulation result through CarSim. The algorithm of finding a proper compensation value is simply using the sensor data that are already mounted on vehicles, such as yaw rate, longitudinal speed, and lateral acceleration. The real vehicle test was conducted to verify the proposed algorithm. From the results, the algorithm can estimate the sideslip angle without unattainable variables.
An aneurysm clip is a medical instrument that is used intraoperatively to clip a ruptured cerebral aneurysm and reduce the risk of rebleeding. To prevent the clips from slipping off the aneurysm neck, it is very important to maintain a constant clamp force. A high frictional coefficient of the clip blades will also help prevent slippage between the clip blades and the blood vessel. In this study, to raise the frictional coefficients of the clip blades, we used a laser processing machine to produce clamp surfaces of the aneurysm clips with micro-dimples or micro-grooves. The static and dynamic frictional characteristics of the clamp surfaces made in this way were examined. The grooved surfaces with a width of 30 μm and a groove pitch of 40 μm showed the highest frictional coefficient. However, the dimpled surfaces with a shallow depth of 1 μm showed lower frictional coefficients than existing aneurysm clips.
A type of foil journal bearings with double-layer protuberant foils as elastic support was studied by numerical analysis and experiments. Two kinds of material (beryllium bronze and stainless steel) with different elasticity were used for the protuberant foils of the bearings. The analyzing model couples the hydrodynamics pressure of the gas film to the elastic deflection of the top foil and the underlying protuberant foils. The hydrodynamics of gas film is described by the Reynolds equation. The top foil and the protuberant foils are modeled as thin plates and the protuberances are treated as rigid support. For calculating the deflection of the top foil, the deflection of the protuberant layer beneath the top foil is taken into account. With a given load, the gas film thickness and pressure are obtained by using finite element method and finite difference method. The key static and dynamic parameters are presented. In experiments, both of the two foil bearings run well in a turbo-expander. The new takeoff and shutoff pressure and speed are proposed for practical operation of the hydrodynamic lubricated high speed turbo-expander. In addition, the synchronous and subsynchronous rotor motions have been tested and analyzed. The experimental tests of the two bearings in a high-speed turbo-expander suggest that the bearing using stainless steel as the foil material shows higher stiffness, which agrees well with the numerical predictions.
This work is an extension of the authors' work where RRSS motion generation and RRSS axode generation were used to produce a spatial cam mechanism (D'Alessio et. al., 2013). Here, a cam system design method is presented where spherical four-bar motion generation and axode generation methods are applied. The primary advantage of the spherical four-bar linkage, compared to the RRSS linkage, is that the former can be scaled without adding error to the positions achieved by its coupler link. As an example, a concept prosthetic knee is developed to precisely achieve a group of prescribed femur positions.
To satisfy the requirements of high accuracy and high-loading capacity, a novel precision-power hourglass worm drive characterizes with backlash-adjustable and wear-compensable is demonstrated. This hourglass worm drive is consisted of an involute helical beveloid (IHB) gear and a toroidal involute (TI) worm generated by the IHB gear tooth surface, and the material of IHB gear is bearing steel, as well as the material of TI worm is structural steel. For this hourglass worm drive, mathematical model is developed, basic equations are derived, and tooth contact analysis (TCA) is simulated by computerized calculation examples. Theory of backlash-adjustable and wear-compensable of this hourglass worm drive is derived. The high-loading capacity of this novel hourglass worm drive is confirmed by the TCA and stress analysis. This study is expected to provide a theoretical foundation for the future industrial application of this novel backlash-adjustable and wear-compensable hourglass worm drive.
Since minor gear damage may cause serious failures of the entire equipment, early detection of gear damage is one of the important measures to prevent the machine system from malfunction. This paper proposes a method of diagnosing early gear damage by analyzing the vibration accelerations of one gear tooth. Gears manufactured with three different kinds of methods are tested in this study. Their tooth profile error is different from each other. Therefore, the influence of tooth profile error to the damage diagnosis is also discussed in this study. The vibration acceleration on the gear box was acquired as the original signal. In order to eliminate the interference components from the original signal, the time synchronous averaging method is adopted to process the original signal. Thus, the time synchronous averaging signal of driving gear is obtained as the analytical signal. Because the abnormal wave is not obvious in the whole signal, the vibration accelerations of one gear tooth was extracted from the time synchronous averaging signal for studying in detail. For illustrating the representative character of the vibration signal, statistical parameters are calculated from the vibration acceleration of one gear tooth to evaluate the conditions of gear tooth. In addition, the coefficient of variation method is employed to evaluate the contribution ratio of these parameters to gear damage and the weight coefficient of each parameter is obtained. The statistical parameters are synthesized into a unified feature based on the weight coefficient. The results show that the unified feature distance of damaged tooth is distinctive from the normal teeth, and the gear damage can be detected by the present method in this study.
Vacuum brazing products have excellent joining quality, less deformation and fewer residual stresses. The vacuum brazing technique has significant effect on the microstructure and property of the aluminum brazed joint, but there is little discussion about the optimization of the process. This study investigates how different process parameters affect the tensile properties of 6061-T6 aluminum vacuum brazed joints. The parameters including the soaking temperature, soaking time, brazing temperature, and brazing time were taken into consideration. Analysis of variance showed that soaking time is the most dominant factor. The optimal process parameters were predicted by Taguchi method to obtain the highest tensile strength. Experimental results indicated that the error between predicted and experimental tensile strength is only 0.33%. It demonstrated that the Taguchi method is feasible for obtaining the optimal process parameters of aluminum vacuum brazed joints. Microstructures, microhardness and fractograghs of the aluminum brazed joints produced by optimal process were also analyzed.
In this study, a novel kinematic analysis procedure of the double wishbone suspension mechanism regarding steering input is proposed. In the previous study, published by the authors, the double wishbone mechanism was investigated disregarding steering input. To the best of our knowledge, there is no analytical method available in the literature for the analysis of double wishbone suspension mechanism regarding steering input. Initially, analysis of the mechanism for variable steering input, while keeping wheel travel fixed is considered. Then, kinematic analysis is performed analytically for the ultimate case of two inputs. Analysis simultaneously for both variable steering and variable wheel travel is presented. The essential parameters; camber, caster, kingpin angles are defined according to the kinematic model. For verification, a synthesized mechanism is established in Catia software and same results with the analytical model are obtained. Another presented novel analytical approach is anti-dive/lift analysis of the double wishbone mechanism.
Based on the space engagement theory and cam theory, an approach of the tooth generation of curve-face gear, concerned the tooth profile equation, tooth characteristics analysis, manufacture and error evaluation is obtained. The tooth surface equation of curve-face gear is obtained and the tooth surface is produced by inserting advanced surface command in SolidWorks combining with the interference analysis. An error evaluation method, based on the extracting points from a series of sections along the tooth length, is put forward. The tooth-flank characteristics, concerned the distribution angle and meshing angle, are analyzed and the interference phenomenon is discussed. Finally, the validity of the theory is demonstrated by the rolling experiment and additive manufacturing.