Experiments were made to study the contact force and frictional force between the magnetic head and the magnetic tape in a two head helical scan type VTR. Both forces were directly measured in the experiment in which the head attached to spring plates contacts with the tape under the conditions of the rest and running at 0.19 m/s. The frictional force at higher speeds was measured by means of the deceleration of disk having heads due to friction. The tension of tape running around the cylinder was also studied in VTR. The frictional force increases linearly with the increase of tape tension and height of head protruded from the cylinder and is of order of 1 g. The friction is independent upon the frictional speed over the range of 0.19 to 11 m/s. It is concluded that the frictional force is directly proportional to the contact force and the coefficient of friction takes approximately the value of 0.22 in operation of VTR. The tape tension at the tape supplying side of the cylinder in VTR is about three times that at the winding side. The increase of tension is mainly due to the friction of tape sliding on the cylinder and decreases as the protruding height of head increases.

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High precision inertial sensors such as gyros and accelerometers are necessary to launch a space vehicle successfully. The gimbls of these inertial sensors which had been developed were floated in damping oil whose density was equal to their average density and the output axes of the sensors were supported by means of high precision jewel-pivot bearings. This type of bearings cannot help having a small clearance between jewel and pivot, therefore the bearings may sometimes occur frictional torque which is uncertain torque about the axes. In order to develop preciser sensors, the axes of the sensors are necessary to be provided with suspension systems which are free from uncertain torque about the axes. A magnetic suspension system is one of the systems which have the above mentioned capability.
Formerly, R. H. Frazier had derived an expression of a magnetic suspension force neglecting the leakage of the magnetic flux which may occur in the gaps between rotor and stator of the magnetic suspension system and neglecting the components of the magnetically nonrestorative force which acts on the gaps' surface. Because the expression had been reasonable only within a small displacement of the output axis, unstability of the magnetic suspension force could not be discussed which exists with the output axis largely displaced in the gaps.
From this point of view, a passive magnetic suspension system with an eight-pole stator is theoretically analyzed, which can be applied to supporting the output axes of the sensors. In this theoretical analysis, the above mentioned analytical imperfections is taken into consideration, and the equation of the magnetic suspension force is directly derived from an equation of the magnetic energy which exists in the gaps, and then static characteristics of the magnetic suspension systems obtained by means of digital computation are discussed. Consequently it is proved that authors' equation can discuss the unstable region of the magnetic suspension force. And then it is shown that authors' analytical results with relation to the magnetic suspension force are in close accordance with Frazier's results within a small displacement of the output axis.

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Some experiments on the frictional resistances of linear ball bearings called ball bushings were performed.
The experimental results obtained are as follows :
(1) The maximum and average values of frictional resistance increase approximateiy in proportion to bearing load.
(2) The maximum and average values in the case of rolling elements contacting with shaft in three-tracks are greater than the values in two-tracks.
(3) The maximum frictional resistance is obtained when rolling elements pass from the load-side to the unload-side in tracks.

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The microstructure of dressed abrasive cutting edges and the transitional behavior of the cutting edges in the initial stage in grinding are investigated by observing directly dressed abrasive cutting edges in detail and by pursuing the behavior of the particular cutting edges in grinding. The relation between the transitional behavior of the cutting edges and the grinding force in the initial stage in grinding is examined by measuring the variations of the cutting edge ratio and the grinding force in grinding.
The conclusions obtained in this study are as follows :
(1) The surface roughness of dressed abrasive cutting edges is approximately flat though the dressed streak is observed on the surface. Accordingly the microunevenness reported previously cannot be found on the surface.
(2) A lot of nondirectional microcracks are observed on the surface. Therefore the surface structure is fragile and the fragile layer is easily removed by the replica operation and in grinding. The microunevenness exists under the fragile layer and is appeared after the fragile layer is removed.
(3) The grinding force and the cutting edge ratio are high in the initial stage in grinding. From these results, it is considered that the flatness of the dressed cutting edges influences the high grinding force in the initial stage with some reason.

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An attempt has been made in this paper to estimate the strength of the grinding wheel by applying linear fracture mechanics to a simplified model. In this model, each of the pores was replaced by a crack whose length is set equal to the sum of the lengths of the pore and the microcracks within the grain or the bond. The grinding wheel structure is idealized as a two-dimensional, isotropic, homogeneous body. Analysis has been carried out on the assumption that the many microcracks do not interefere with one another and that only the crack which is perpendicular to the loading direction and which has the maximum length need be considered. From the analysis of this simplified model, the following results were obtained :
(1) The equivalent crack length within the grinding wheel structure depends on the grain sizes and is independent of grade.
(2) The bursting speed can be estimated from the K_Ic values determined in static bending tests and tension tests. These two test methods provide upper and lower bounds respectively for the bursting speed.

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Servo or torque-rebalance accelerometers using the principle of feedback have beendeveloped in such countries as the U.S.A. and the U.K. The advantages that the accelerometers have over the instruments with mechanical springs as the force-to-displacementtransducer is the wider dynamic range and less cross-coupling error. However it is supposedthat no report on the development of such accelerometers was made so far in this country.This paper presents the development of a floated pendulum accelerometer with its analog ordigital servo circuit. The reason why we started with the accelerometer of floated pendulumtype is that the components and compositiori of the accelerometer are similar to those of asingle-degree-of-freedom rate integrating gyro which was developed earlier in our laboratory.Several considerations for designing the floated pendulum accelerometer, and construction forboth an analog and a digital circuits are followed by method of testing the accelerometerwith either an analog or a digital circuit and by the results of the test.

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This paper presents two new mechanical methods in the stroboscopic holographic vibration analysis. In one of the two, the oscillating mirror of the electromagnetic oscillograph is used, and in another, the pulse-motor is used. The mirror oscillating sinusoidally reflects the laser beam and the vibrated laser beam is strobed by the slit. The pulse-motor rotates by the constant angle when one pulse is given and the laser beam is strobed by the slits attached to the motor. As the oscillating mirror and the pulse-motor are driven by the signal that is the input to the vibrator of the subject, or the transformed one, it is easy to synchronize the strobing to the vibration of the subject and the strobing can be synchronized to the signal detected from the vibration of the subject. Particularly, the method using the oscillating mirror is easy, cheap and one of the mechanical methods that can be used in the highest frequency. The vibration patterns of the circular plate clamped at the center and the loudspeaker are got by those methods.

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