春浅いみちのくの精密工学研究室の一机をはさんで学会誌小特集について語り合うQとA.

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本稿では無人化指向の中で,高品質の確保という面を主体にまとめたが,QCDをハイレベルに達成するというユーザの要求にこたえるためには,幅広い面できめ細かい技術の積み重ねが必要である.急速に進歩する制御技術と,基礎的技術の高度化をあわせ,より深くバランス良くとり入れて行くことにより,工作機械の進歩はさらに加速して行くものと思われる.

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上にみるように,質量の動的測定方法を採用すれば,はかりの品物皿や指針の振動が静止するのを待つ必要がない.また,振動測定法のように幾周期もの波形のデータも不要である.信号生成過程のダイナミックモデルを活用すれば,短時間の観測データからでも,質量の推定が行える.つまり,測定の高速化が図られることがわかる.この方法を実施するたたには,はかり部(質量一荷重変換機構)の運動状況を表す加速度,速度,変位などを検出するたたの数種のセンサと,観測信号処理を実行するマイコンが必要である.また,数種類のセンサを用いる場合,それぞれのダイナミックスの違いに注目し,それらをうまく補償することも大切である.しかし,それはソフトウェアの世界で解決できる問題である.すなわち,それぞれの観測信号に対して,その生成過程のダイナミックモデルを構築し,それを踏まえたディジタル信号処理のアルゴリズムを設計すればよいからである.
本稿で紹介した速度,変位検出形質量動的測定システムは,先に提案した速度,変位検出形質量動的推定アルゴリズムの実用性を確認するたたに試作されたものである.動的測定方法の考え方に従えば,このほかにも幾種類もの質量推定アルゴリズムを導出することができる.それぞれのアルゴリズムの特徴を生かし準応用指向型の研究と,実際問題への適用が今後に残された課題である.

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本解説では,高速信号処理システムのVLSI実現において考慮すべき基本的要件について述べた.それらの要件を考慮して,演算回路レベルとシステムレベルにおいて,それぞれに適した高速アルゴリズムとシステムアーキテクチャがあることを明らかにした.また,計算量が少ないために従来よく用いられている信号処理アルゴリズムは,VLSI実現を前提とすると必ずしも効率的ではないために,信号処理アルゴリズムとシステムを新たに開発する必要があることを示した.
ここでは,高速信号処理のVLSI実現の際の基本的考え方を中心にしたため,個々の高速信号処理アルゴリズムについては言及しなかった.これらの詳細に関しては,下記参考文献を参照されたい.

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An apparatus for the measurement of Young's modulus and its thermal coefficient has been newly developed. Both the tension and bending methods are available in this apparatus. The elongation in the tensile test or the deflection in the three-point bending test is detected by using a specially designed sample holder together with a He-Ne laser interferometer with an accuracy of better than 0.1 μm. This apparatus is especially suitable for such thin specimens as leaf springs and hair springs which are often used in precision machines or measuring instruments. The minimum size of specimen to be measured is 0.1 mm in diameter or 5 μm in thickness. Young's modulus of ordinal materials can be measured with an accuracy of better than ±3% in 95% confidence interval. Young's moduli measured by the tension method and bending method were compared with each other and the result showed a good agreement. Thermal coefficients of Young's modulus of six kinds of spring materials were also measured by means of the bending method in the temperature range between 0°C and 50°C.

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This paper describes the non-contacting measuring method of the circumferential vibration of gears by using the double-aperture method, in which a coherent laser beam is directed perpendicular to the side face of the tested gear, and the scattered reflected light is passed through two small apertures and the resultant interference stripes are directly detected with a photo-multiplier to measure the vibration in real time. It was found that the circumferential vibration due to the engagement of gear teeth can be measured by this method with the same accuracy as that by the traditional strain gage method.

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A convenient method for designing bolted joint structures has been developed. At first the model for replacing the practical bolted joint with the structural model constructed by spring and beam elements is proposed. The model has been analyzed by finite element method in consideration of separation behavior at bearing surface among clumped plates. Some experiments are also carried out under the same condition of the above model. The obtained results are follows:(1) Calculated axial stress and bending stress in the relation to the load on the clamped plate are almost consistent with the experimental ones. (2) The increasing rates of axial stress and bending stress on the bolt were inverse proportion to the initial tightening force. (3) when the load were acting on the plate, the increasing rates of axial stress and bending stress on the bolt decreased:(i) with increase in the interval length between bolt axis and plate end or (ii) with decrease in the interval length between bolt axis and application point of load on the plate.

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The purpose of this investigation is to make clear the generation mechanism of polygonal hole which is frequently observed in boring with multi-edged tools, e. g. reamers, core drills, etc. The dynamic stability of multi-edged tool during boring is analyzed using Nyquist's chart in consideration of the regenerative effect, the variation of undeformed chip thickness by the displacement of tool head in the primary cutting direction of each tool edge and the action of dynamic cutting force in the radial direction of each edge. From the theoretical results, in boring with Z-edged tool the chatter vibration occurs at the frequency of about nZ+1 or nZ-1 cycles per revolution of workpiece, where n is an integer and Z is the number of cutting edges. These results agree with the experiments. The influences of cutting condition and tool design on this vibration are also discussed.

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This paper deals with the theoretical analysis of the machining accuracy in end mill operations. The accuracy is defined by the static stiffness of an end mill and the instantaneous cutting force. The static stiffness of an end mill with two helical cutting edges is theoretically analyzed by transfer matrix method. The instantaneous cutting force generated during cutting is calculated by an instantaneous depth of cut at any point of a cutting edge. The results obtained are as follows : (1) Up milling is better than down milling from the point of view of the accuracy. (2) The variation of feed, width of cut and helix angle of the cutting edge has a considerable effect on the accuracy. However, depth of cut has almost no effect on it in the usual operations. (3) Up milling produces a cross section of the workpiece with a convex shape, while down milling produces one with a trapezoidal shape.

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In order to clarify the effect of atmosphere on chipping, high speed face milling tests were carried out on stainless steel SUS 304 with carbide tool P 10 in the sealed chamber reported before. Nitrogen, argon, carbon dioxide and oxygen gases were used as the atmosphere. The main results obtained were as follows : (1) Severe chipping occurred under nitrogen gas atmosphere compared with that of argon gas. On the other hand, no significant chipping was found under carbon dioxide atmosphere. Fe, Cr and Ni were detected on the crater wear surface when milling in nitrogen, argon or carbon dioxide gases, and the chipping increased with the increase of the adhesion of those elements. (2) In the case of milling in oxygen gas, the mean value of chipping wear was almost the same as that in argon gas, while the variance of chipping was smaller than that in argon gas and oxide of Cr-Mn was found on the crater wear part. (3) The variance of chipping increased with the decrease of oxygen content in argon or nitrogen mixed gas.

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It has been shown in our experiments that the grinding performance of the Resinoid Bonded CBN grinding wheel depends on TSUKIDASHIRYO. TSUKIDASHIRYO herein is referred as the distance of the grinding edge of the grains to the bond on the grinding wheel surface. It was found that the grinding performance reaches its maximum when this TSUKIDASHIRYO is about 30 μm. The grinding ratio was more than 250 times as much as that of an ordinary grinding wheel, while the wheel life (the time the surface roughness exceeds 3 μmR_z) was over 40 times longer. It was also found that as long as the grain depth is correct, any material can be ground effectively whether it is untreated or hardened material of SCM 435, or chilled iron. The wheel was first dressed in order to create the desired TSUKIDASHIRYO in the experiments, and it was found that the wheel surface was subjected to "damage" by dressing. However, this "damage" effect lessened as grinding and truing (carried out when the surface roughness deteriorated) were successively repeated, and the grinding ratio and the grinding amount between truing operations increased.

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In a grinding process in which the grain edge fracture predominates over its attritious wear, the dependence of the fracture characteristics upon the grain depth of cut must be taken into account for better understanding of the grinding process, since the depth is not constant but varies with relative location of the grain edges on the wheel surface. Therefore, the effects of grain depth of cut upon the onset probability of the edge fracture, the height loss of the grain tip, and the transition probability of the edge shape are investigated. From a fracture test of WA single grain, of which test method was reported in the previous paper, the probability density of the height loss for a constant grain depth of cut is found to be conformed with a gamma distribution. Another fracture test with a special model wheel having 125 abrasive grains on a certain circumferential line is also conducted, and it reveals that the fracture onset probability and the height loss are proportional to the grain depth of cut. Their proportional constants are obtained experimentally as the maximum likelihood estimator. Two series of fracture tests of single grain under the same grinding conditions but with different grain depth of cut are further conducted, and they reveal that the transition probabilities of the grain edge are independent of grain depth of cut.

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Proper chip breaking performance is always important for safety, easy for chip disposal and efficient in an automatic machining operation. There are various designs of chip breakers available. Unexpected chippings occur on the minor cutting edge of the tool insert which cause the damage of the machined surface and decrease the accuracy of workpieces, even if chip breaking performance is suitable. It is interesting to know the reason why chippings occurred frequently when an insert having proper chip breaking performance was under optimum cutting conditions. Using four integral obstruction types of chip breakers, remarkable differences were found in up-curl chip formation and the occurrence time of chipping, where the amount of flank wear ( VB) and crater wear (KT) were nearly same. The appearance of chipping on the minor cutting edge becomes faster as the chip-breaker distance decreases. It was found through contour observation that the sharpened edge could no longer withstand the dynamic components of cutting forces and resulted in chipping of the cutting edge due to an increment of the minor cutting edge angle.

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Single point diamond dressers (sharp-edged type and worn-edged type) and impregnated dressers (fine grain diamond type with hard bond and diamond powder type with soft bond) are taken up, and the following two effects are discussed : macro effect (transferability of dresser profile on the wheel surface) and micro effect (sharpness and distribution density of grain cutting edges). The macro effect is investigated by means of dressing simulation and power spectrum analysis, and the micro effect is investigated by means of scratch method. In addition, grinding forces are measured of cylindrical plunge grinding. The results are summarized as follows : (a) The transferability can be evaluated by the power ratio and higher power ratio means better transferability. Impregnated dresser, which is superior in the transferability to single point diamond dresser, shows worse sharpness of grain cutting edge and brings higher grinding force. (b) When using single point diamond dresser, index number n of grain cutting edge distribution pattern changes from n=2 (parabolic) toward n= 1 (triangular) because of the micro effect with an increase in the dresser feed rate. When the macro effect appears on it, the index number n increases and the density decreases.

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Factors of machining error in end milling are analyzed from a systematic point of view. Supposing that the machining error in end milling consists of the geometric error of a machine tool, deflection of the machine-tool structure, the tool holder and the end mill, thermal expansion of the end mill, and the error caused by tool wear, built-up edge and so on, the relation between these factors and the resultant machining error is formulated. Based on this formulation, errors of workpieces machined under 18 different experimental conditions are measured and processed to evaluate the amount of individual error components separately. The result obtained are as follows : Nearly a half of the error is due to the deflection of the end mill. The deflection of the jointed parts existing at tool holder-spindle connection and end mill-tool holder connection is not proportional to the cutting force, and can not be neglected. Thermal expansion of the end mill increases with the progress of cutting.

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This paper describes the principle, prototype design and experimental evaluation of the performance of a new balancer system developed for automatic compensation of the dynamic unbalance of a grinding wheel. The system consists of a high response micro-delivery injector and a twenty-four-chambered pocketed ring. The balance accuracy equals the product of the mass of unit quantity of the liquid injected for every revolution of the wheel and the radius of pocketed ring. Characteristics of a prototype balancer has been found experimentally to well follow the theoretical prediction and the system is capable of suppressing the wheel head vibration to less than 0.01, μm amplitude.

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