Hisashi Nakamura

A high-precision positioning servo controller based on phase/frequency detecting technique of two-phase-type PLL

This paper presents a new method proposed for high-precision positioning servomechanisms. The servo controller uses a two-phase-type phase-locked loop (PLL) to detect position tracking error and speed fluctuation with high resolution. Because the two-phase-type PLL has a wide frequency range and high noise suppression performance, we applied the new controller to high-power and high-velocity servo-spindles and achieved high control performance. The developed servo-spindles were used by a high-productivity numerically controlled gear grinding machine. Experiments of gear grinding were carried out, and the results confirmed the performance of the developed controller.

Characteristic regimes of premixed gas combustion in high-porosity micro-fibrous porous media

Dynamical behaviour of the premixed flame propagating in the inert high-porosity micro-fibrous porous media has been studied numerically. Effects of mixture filtration velocity, equivalence ratio and burner transverse size on the flame structure have been investigated and the regions of existence of different combustion regimes have been determined. It was found that the influence of the hydrodynamic instability on the flame dynamics is significant in the case of the moderate and high filtration velocities and this effect is negligible at the low velocities. At the moderate filtration velocities the effect of hydrodynamic instability manifests in the flame front deformation and in particular in the flame inclination. It was found that the flame can be stabilized within the whole interval of the filtration gas velocity, whereas in the ordinary porous media the standing wave is settled only at fixed value of gas filtration velocity. This finding is in line with recent experimental results on combustion in micro-fibrous porous media (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16). Possible physical interpretation of the flame anchoring effect may be given on the base of present numerical analysis. At the high filtration velocities the hydrodynamic instability manifests itself in periodical appearance of the moving wrinkles on the flame front surface which forms non stationary high temperature trailing spots behind the leading part of the flame front. Such dynamics may be associated with splitting wave structures which were revealed in previous experiments (Yang et al., Combust. Sci. Tech. 181 (2009), 1–16).

Filtration Combustion of Methane in High-Porosity Micro-Fibrous Media

Filtration combustion of lean methane-air mixtures in inert, high-porosity micro-fibrous media was studied experimentally in quartz tubes with different diameters. First, an overall stability diagram was obtained. Between the upstream and downstream propagating regimes, a specific rigid standing wave regime was observed, whereas only one standing wave point existed in other ordinary porous media. A specific instability phenomenon of a combustion wave splitting into two or more parts during wave propagation downstream was also observed in smaller diameter tubes at high filtration velocities. In principle, the results of a conventional two-temperature 1D analytical model captured the main feature of the process obtained in the experiment, but failed to explain the process of flame anchoring to the porous carcass that was observed under variation of the mass flow rate. The possible causes of the failure of the conventional modeling approach were presented.

Measurement of Supersonic Flow Field using Particle Tracking Velocimetry

An oblique shock wave in a supersonic flow field was measured and visualized using Particle Tracking Velocimetry (PTV). The beginning of the velocity drop at the shock wave was sharper than that detected by general Particle Image Velocimetry (PIV). The location of the shock wave in the obtained velocity vector was in good agreement with that in Schlieren images because PTV has the advantage of high spatial resolution. The statistical values of turbulence in the airstream were successfully estimated. Another advantage of PTV is low calculation load. Real-time PTV was developed in this study. The image capture and the tracking calculation were performed in real time and the obtained vector data were sent to another computer using a network socket. It is considered that the transdisciplinary approach between experiment and numerical simulation can be performed using velocity vectors which will be sent to a supercomputer in real time. It is conformed that the obtained vector data and the real-time PTV are capable of realizing a transdisciplinary measurement system in future.

Development of a Wheel Spindle for a Productive Type Gear Grinding Machine

The authors have developed a wheel spindle with an in-built brushless motor for a transmission gear grinding machine to be used in a production environment. The spindle is capable of rotating at low or high speeds with high torque. The maximum rotary speed is 10 000 r/min and its rated torque is 8 Nm. In such high power systems, ordinary interpolators cannot be used to monitor the rotary angle of the shaft due to the intensity of switching noise from the servo-amplifier. To overcome this problem, an interpolator using a two-phase type PLL developed by Emura was used with additional inductive chokes to reduce switching noise. Initial experimental results have shown that this type of wheel spindle is well suited to gear grinding in production environments.

Progressing a Productivity of Gear Grinding

This paper describes how to progress a productivity of gear grinding. We mention the development of a productive type CNC gear grinding machine using high-speed wheel spindle for screw-shaped CBN wheel and introduce some results of grinding test.

Evaluation of the reactivity of ultra-lean PRF/air mixtures by weak flames in a micro flow reactor with a controlled temperature profile

ABSTRACT The reactivity of ultra-lean primary reference fuel (PRF)/air mixtures was investigated by weak flames in a vertical-type micro flow reactor (MFR) with a controlled temperature profile. In experiments, steady-separated weak flames were obtained at equivalence ratios between 0.5 and 1.0 for PRF80, 90, and 100. At leaner conditions, all the fuels showed hot flames at lower temperature regions, indicating higher reactivity. In one-dimensional steady simulations of the present micro flow reactor by modified Chemkin-Pro PREMIX, the LLNL PRF mechanism was able to reproduce the experimental tendency, while the KUCRS PRF mechanism showed the opposite trend. By analyzing major reactions leading to the hot flame, seven H–O reactions were identified that primarily control the hot flame response to a change of equivalence ratio. By exchanging the rate parameters of these seven reactions for more recent ones, the reactivity trend was brought to very good agreement with experimental results. This improvement was credited to a better spatial separation of intermediate- and high-temperature reactions in the MFR and emphasizes the strength of this investigation method.

Effects of n-butanol addition on sooting tendency and formation of C1 –C2 primary intermediates of n-heptane/air mixture in a micro flow reactor with a controlled temperature profile

ABSTRACT Effects of n-butanol addition on the sooting tendency and formations of C1 and C2 primary intermediates of n-heptane/air mixtures were studied in a micro flow reactor with a controlled temperature profile. Sooting tendency was investigated over equivalence ratios of 1.5–4.0 at a maximum wall temperature of 1300 K. Experimental observations indicated two types of flames: a flame alone (type I) or a flame with soot (type II). The critical sooting equivalence ratio, at which the flame switched from type I to type II, increased with the increase of butanol content in the fuel blend. Results show that the sooting tendency of n-heptane decreases as the amount of n-butanol is increased. Computational results obtained using the Chemical Reaction Engineering and Chemical Kinetics mechanism show fair agreement with measurement results obtained at equivalence ratio of 2.0 and the maximum wall temperature of 1166 K. The validity in initial-stage reaction progress of existing mechanisms was examined.

OH-LIF measurement of H2/O2/N2 flames in a micro flow reactor with a controlled temperature profile

This paper presents combustion and ignition characteristic of H2/O2/N2 flames in a micro flow reactor with a controlled temperature profile. OH-LIF measurement was conducted to capture flame images. Flame responses were investigated for variable inlet flow velocity, U, and equivalence ratio, . Three kinds of flame responses were experimentally observed for the inlet flow velocities: stable flat flames (normal flames) in the high inlet flow velocity regime; unstable flames called Flames with Repetitive Extinction and Ignition (FREI) in the intermediate flow velocity regime; and stable weak flames in the low flow velocity regime, at = 0.6, 1.0 and 1.2. On the other hand, weak flame was not observed at = 3.0 by OH-LIF measurement. Computational OH mole fractions showed lower level at the rich conditions than those at stoichiometric and lean conditions. To examine this response of OH signal to equivalence ratio, rate of production analysis was conducted and four kinds of major contributed reaction for OH production: R3(O + H2 H + OH); R38(H + O2 O + OH); R46(H + HO2 2OH); and R86(2OH O + H2O), were found. Three reactions among them, R3, R38 and R46, did not showed significant difference in rate of OH production for different equivalence ratios. On the other hand, rate of OH production from R86 at = 3.0 was extremely lower than those at = 0.6 and 1.0. Therefore, R86 was considered to be a key reaction for the reduction of the OH production at = 3.0.

Soot and PAH Formation Characteristics in a Micro Flow Reactor With a Controlled Temperature Profile

To examine soot and PAH formation processes for rich methane/air and acetylene/air mixtures, a micro flow reactor with a controlled temperature profile was employed. In the experiment for a methane/air mixture, four kinds of responses to the variations of flow velocity and equivalence ratio were observed as follows: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither flame nor soot formation. Soot formations were observed in low flow velocity and high equivalence ratio. Starting point of soot formation shifted to the upstream side, i.e., low-temperature side, of the micro flow reactor with the decrease of flow velocity. One-dimensional steady-state computation was conducted by a flame code. In high flow velocity, low mole fraction of C2 H2 and high mole fraction of OH were observed in the whole region of the micro flow reactor. Soot volume fraction did not increase in this case. On the other hand, in low flow velocity, high mole fraction of C2 H2 and low mole fraction of OH were observed at the downstream side of the micro flow reactor. Soot volume fraction increased in this case. Since significant soot formation was observed at the low flow velocity and the high equivalence ratio, experiments with gas sampling were conducted for acetylene/air mixture to investigate temperature and equivalence ratio dependence of soot precursor production in such condition. Volume fractions of benzene increased with an increase of temperature. They were larger at higher equivalence ratio at the same temperature. Volume fractions of styrene increased with an increase of temperature. They were larger at higher equivalence ratio when the temperature is less than 1000 K. However the tendency was changed at 1000 K, styrene volume fraction at equivalence ratio of 7.0 was larger than that at equivalence ratio of 8.0.© 2011 ASME