Patent Publication Number: US-4221937-A

Title: Moving iron type cartridge

Description:
The present invention relates to MI-type cartridges, i.e., to cartridges of the so-called &#34;moving iron&#34; type. 
     A conventional cartridge of the kind referred to herein has been constructed, for example, as shown in FIG. 1. In FIG. 1, 1 is a yoke for a right channel, 2 is a yoke for a left channel. A cantilever 4 with a stylus at its end which is integrated with a magnetic member 5 and held by a mounting base (not shown) through a damper 6 is placed in a space 3 surrounded by the end portions of said two yokes 1 and 2 which extend longitudinally approaching to each other. In the vicinity of said magnetic member 5, a permanent magnet 7 is arranged to magnetize the magnetic member. In this construction, however, as the cantilever 4 is located in a narrow space 3 defined with the end portions of the yokes 1 and 2, the replacement of a worn-out stylus is forced to be extremely troublesome. Furthermore, a mechanical pressure is likely to be applied to the yokes 1 and 2 which are usually made of mu metal, when the stylus is replaced with a new one, so that the magnetic characteristics of the yokes are caused to change and accordingly performance of the cartridge may become gradually inferior. 
     When employed in a power generation mechanism, the magnetic member 5 of the cantilever 4 is to oscillate within a narrow space 3, not providing a sufficient moving range in the design and, consequently, it is difficult for the mechanism to obtain outputs of a high level. 
     The present invention has been suggested so as to eliminate the abovementioned defects. 
     The principal object of the present invention is to provide an MI-type cartridge in which the stylus replacing operation can be easily performed. 
     Another object of the present invention is to provide an MI-type cartridge which is able to give outputs of a high level, 
     A further object of the present invention is to provide an MI-type cartridge in which the follow-up characteristics of the stylus is excellent. 
    
    
     Other objects and effects of the present invention shall be made clear upon reading the following detailed description of the present invention along preferred embodiments with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a conventional cartridge; 
     FIG. 2A is a perspective view of an MI-type cartridge according to the present invention; 
     FIG. 2B is a perspective view showing only the internal mechanism of an MI-type cartridge; and 
     FIGS. 3A, 3B, 4A, 4B, 5A and 5B are explanatory drawings of the operation of the cartridge according to the present invention. 
    
    
     In FIGS. 2A and 2B, 11 and 12 are permanent magnets for the right and left channels respectively. The magnets are magnetized into N pole at one end and S pole at the other end respectively and further provided respectively with two pairs of yokes 13, 13a and 14, l4a at the ends of the permanent magnet 11, whereas two pairs of yokes 15, 15a and 16, l6a are provided at the ends of the permanent magnet 12. 
     The permanent magnets 11, 12 and the base portions of the yokes 13, 13a, 14, 14a, 15, 15a, 16 and 16a are connected to and integral with a mounting base 22 of a synthetic resin. The magnets 11, 12 are mounted on two mounting planes 22A, 22B of the base 22. The respective pair of the yokes 13 and 14, 13a and 14a, 15 and 16, and 15a and 16a which are connected to the permanent magnets 11 and 12 extend to approach each other at the end surfaces. The end surfaces 13&#39;, 13a&#39; and 14&#39;, 14a&#39; of the two pairs of yokes 13, 13a and 14, 14a which are attached to one permanent magnet and the end portions 15&#39;, 15a&#39; and 16&#39;, 16a&#39; of the other two pairs of yokes 15, 15a and 16, 16a attached to the other permanent magnet are arranged so as to terminate on the respective same planes defined respectively by end surfaces A of yokes 13, 13a, 14, 14a, and end surfaces B of yokes 15, 15a, 16, 16a. 
     The two planes on which the respective end portions of the yokes of said right and left channels are arranged, make an angle of 45° respectively with respect to the surface of a phonograph record (not shown), and further make an angle of 90° with respect to each other. 
     A cantilever 17 which is integral with a magnetic member 18 and held on the mounting base 22 through a damper 19 is arranged to oscillate freely within a region defined by the two planes making an angle of 90° with respect to each other as described above. 
     The damper 19 is inserted into and fixed to a damper case 24 which is attached to the mounting base 22 with screws 23. 
     The cantilever 17 and the magnetic member 18 aligned therewith are arranged to be substantially parallel in the axial direction to said planes in the stationary state, whereas to oscillate in response to the action of the stylus when a phonograph record is played. The yokes 13-16a can be made of a so-called laminated material according to demand. Coils 20 and 21 are wound appropriately on the yokes 13-14a for the right channel and on the yokes 15-16a for the left channel respectively for inducing a current in response to a change of the magnetic flux passing through the yokes. In the embodiment illustrated, the coil 20 is wound clockwise on the yoke 13 fixed to the N pole side of the permanent magnet 11, then wound counterclockwise on the opposite yoke 14 on the S pole side, further counterclockwise on the yoke 14a opposing to the yoke 14 on the S pole side and then again clockwise on the yoke 13a on the N pole side opposite to said yoke 14a. The coil 21 is wound on the yokes 15-16a in the same manner as described above. In short, the coils 20, 21 are wound not to cancel but, to superpose currents induced electro-magnetically in response to the change of the magnetic flux passing through the yokes 13-16a. It is easily understood that the holding mechanism of the cantilever 17 is constructed substantially in the same way as in the conventional cartridges. 
     Hereinafter, the operation of the cartridge according to the present invention will be described in detail. The right and left channels are constituted substantially in the same way, therefore the description will be given only to the right channel. FIGS. 3A and 3B show the cartridge in a stationary state wherein the magnetic flux from the N pole of the permanent magnet 11 passes through the yoke 13, the end portion 13&#39; of the yoke 13, the magnetic member 18 of the cantilever 17, the end portion 14&#39; of the yoke 14, and the yoke 14 reaching the S pole of the permanent magnet 11. Also, the magnetic flux from the N pole of the permanent magnet 11 passes through the yoke 13a, the end portion 13a&#39; of the yoke 13a, the magnetic member 18 of the cantilever 17, the end portion 14a&#39; of the yoke 14a, and the yoke 14a reaching the S pole of the permanent magnet 11. In this state, there will be caused no change in the flux flow, and through the coil 20 there flows a constant magnetic flux in the reverse direction inducing no electromotive force. 
     On the other hand, FIGS. 4A and 4B show a case wherein the cantilever is moved in a certain direction P1. In this case, a magnetic circuit is formed through the end portions of yokes 13&#39; and 14a&#39; located symmetrically with respect to the damper 19, that is, the flux passes through tye yoke 13, the end portion 13&#39; of said yoke 13, the magnetic member 18, and the end portion 14a&#39; of the yoke 14a, inducing an electromotive force in the clockwise direction with respect to the flux flow. At the same time, in the yoke 13a from which the magnetic member 18 is separated the flux is suddenly reduced, inducing a counter electromotive force and thus providing outputs of a sufficiently high level between both ends of the coil 20. 
     In the case shown in FIGS. 5A and 5B, if the cantilever 17 is moved in the reverse direction P2 to the direction in the case of FIGS. 4A and 4B, the flux flows through the yoke 13a, the end portion 13a&#39; of the yoke 13a, the magnetic member 18, and the end portion 14&#39; of the yoke 14 inducing in electromagnetic force in the clockwise direction with respect to the flux flow. At the same time, in the yoke 13 from which the magnetic member 18 is separated, the flux is suddenly reduced, inducing a counter electromagnetic force and thus providing outputs of a sufficiently high level between both ends of the coil 20. If the polarity is reversed to the case as shown in FIG. 2 and correspondingly the winding direction is altered, the same effect may be obtained. 
     According to the MI-type cartridge constructed as mentioned above of the present invention, the following effects can be obtained; 
     (I) The cantilever is located in a region defined by two planes on which the end portions of the two channels are arranged and opened on the other lower two sides, therefore, the stylus replacement is far easier than in the conventional cartridge wherein the cantilever is located in a narrow space defined by the end portions of the yokes. 
     (II) The yokes are arranged only on two planes with respect to the cantilever, therefore, there exists no possibility of applying a mechanical pressure to the yokes when the cantilever is mounted and dismounted. 
     (III) The oscillation space for the cantilever can be secured sufficiently large and, accordingly, a power of higher level can be obtained. 
     (IV) The cantilever 17 is integrated with only the magnetic member 18. Further the magnetic member 18 can be made of a light metal of a high magnetic permeability such as sold under the name &#34;Permalloy&#34; to reduce the gross weight of the cantilever and the mass to a large extent. Accordingly, not only the stylus can be protected from wearing-off but also the follow-up characteristics of the stylus can be improved extraordinarily. 
     (V) The durability of and the reliability on the cartridge will be increased due to that outputs of a high level can be obtained with a high efficiency. 
     (VI) The magnetic member of the cantilever is to be excited powerfully and, thereby, a large output voltage can be obtained.