Journal of the Horological Institute of Japan

The present report relates to a new small synchronous motor, unidirectional selfstarting synchronous motor which comprises a permanent magnet rotor made of ferrite with magnetic poles of alternate polarity on the cylindrical Periphery and a stator with a group of many poles enveloping a field coil and extending alternately in the shape of teeth from the both sides of the coil into the inside, the said group of poles composing unshaded poles alternately with another group of poles which forms shaded poles having flux phase difference by means of a shading plate. The shaded poles have flux phase difference of 40 - 45 electrical degrees and by making the amount of flux shift of the unshaded poles 130 - 140 electrical degrees. unidirectiona1 self-starting is assured. Its principle, structure, properties. characteristics and use are described. Emphasis is placed upon the fact that the great defects in the starting property, noise, life etc, as seen in tradional motor of this kind because of their having inversion preventing mechanism are all removed, so that these motors can be made smoller and the structure extremely simphified.

View full abstract

Show abstractHide abstract

A theoretical study has been made of the vibration mode in a U shape tuning fork which consists of a semicircular yoke and two straight prongs. In such a fork, the following relation is in exist:n_j=κ(M_j/l)^2√8(E/ρ) where n_j the resonance frequency of jth order vibration mode of the tuning fork. l the total length of the median line, κ the radius of gyration of the section, E and ρ, Young's modulus and density of the material, respectively, and m_j a dimensionless constant connecting the above quantities to each other. When r, the radius of the semicircular yoke, l_1 , the length of the prong, and, k and Q are defined as follows:k=2r/(r+l_1), Q=(k/l)^2, m_j is, in general, the function of k and Q. And, it is confirmed that m_j depends only on k at the lower modes of the vibration in the ordinary tuning fork. Therefore, the numerical value of m_j is presented with the various values of k. According to wheather j is odd or even. the vibration mode is symmetric or not. When j=1, 3, the vibration mode is symmetric and the node of the vibration does not exist anywhere along the median line. The position wi[h the minimum amplitude in the yoke is indicated as the function of k in the report. When j= 2. thc vibration mode is not symmetric and the position with minimum amplitude exists in the middle point of the yoke. ln a particular casc of k≒0.38, the amplitude becomes zero in the point. Some of the above theoretica1 results are ascertained in the present experiment.

View full abstract

Download PDF (967K)

Register with J-STAGE for free!