Abstract:
A pickup cartridge composed of a cantilever, a plate-shaped armature and a magnet or magnetic material. The plate-shaped armature is pivotally mounted to the cantilever and stretched backward by a suspension wire through a damper disposed in front of the magnet or magnetic material. A holding means is disposed at the rear of the damper and includes a magnet with north and south poles. Coils are mounted on the armature. The magnetic flux which passes through the coils passing in the direction of the axes of the coils, but not parallel to the direction determined by a line between the north and south poles of said magnet, produces a linear push-pull output.

Description:
This is a continuation, of application Ser. No. 639,189, filed Dec. 9, 1975, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a moving coil type pickup cartridge, and particularly to a pickup cartridge which can be made small in weight with a magnetic pole being simply constructed and can simultaneously improve magnetic characteristics of an armature. 
     2. Description of the Prior Art 
     As a prior art moving coil type pickup cartridge (hereinafter referred to simply as a pickup), a pickup such as shown in FIG. 1 has been disclosed in U.K. patent specification No. 1,000,035 and the like. In this pick-up, a plate-shaped armature 2 is pivotally mounted to a cantilever 1 at its back and wound thereon with left and right coils 3a and 3b in such a pattern as shown in FIG. 2. The armature 2 is fixed to a magnetic pole 5 with a damper 4 being glued to its back. A suspension wire 7 is fixed at its one end at the inside of a hollow portion 6 of the cantilever 1, while a fixed member 9 is inserted in a spot facing aperture 8 bored in the magnetic pole 5 and this fixed member 9 has provided therein a bore 11 through which a pipe 10 for fixing the other end of the suspension wire 7 is inserted. Reference numeral 12 designates a set screw for fixing the fixed member 9 to the spot facing aperture 8 of the magnetic pole 5. Reference numeral 13 represents another magnetic pole having a bore 14 through which the cantilever 1 is extended. With the prior art pickup as mentioned above, the coils 3a and 3b on the armature 2 disposed between the magnetic poles 5 and 13 cross the parallel magnetic field therebetween to generate an electromotive force. 
     However, in the prior art example constructed as described above, if the cantilever 1 is greatly moved laterally or vertically, the cantilever 1 butts against the wall of the bore 14 of the magnetic pole 13 resulting in its breakage. Further, with the magnetic poles of such a configuration it is difficult to form the uniform parallel magnetic field. Therefore, there is a drawback such that if the uniform parallel magnetic field is not formed by the magnetic poles, the crosstalk between right and left channels is increased. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of this invention to provide a pickup free from the above described drawbacks. 
     It is another object of this invention to provide a pickup based upon a novel electromotive force generating principle such that the construction of a magnetic pole is simplified and decreased in weight with an armature being not disposed within a parallel magnetic field between magnetic poles; and also non-linearity due to magnetic characteristics of the armature is canceled by push-pull effect to improve its linearity. 
     The other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view showing a main portion of a prior art pickup; 
     FIG. 2 is a plan view showing an armature used in the pickup of FIG. 1; 
     FIG. 3 is an exploded perspective view showing one embodiment of a pickup according to this invention; 
     FIG. 4 is a cross-sectional view showing the main part of FIG. 3; 
     FIGS. 5A, 5B and 5C are cross-sectional views respectively used for explaining the electromotive force generating principle of the pickup according to this invention; 
     FIG. 6 is a graph showing characteristic curves of inclination of the armature versus magnetic flux passing through the coil of the armature in this invention; 
     FIG. 7 is a perspective view showing another embodiment of the magnetic pole of this invention; 
     FIG. 8 is a cross-sectional view of the magnetic pole of FIG. 7; 
     FIG. 9 is a corss-sectional view showing a further another embodiment of the magnetic pole of this invention; 
     FIGS. 10 and 11 are perspective views respectively showing another embodiments of the magnetic poles of this invention; 
     FIG. 12 is a cross-sectional view showing a further embodiment of this invention; 
     FIG. 13 is a perspective view showing a magnetized condition of the magnetic pole used in the embodiment of FIG. 12; 
     FIGS. 14A, 14B and 14C are cross-sectional views used for explaining the electromotive force generating principle of the embodiment shown in FIG. 12. 
     FIG. 15 is a perspective view showing another embodiment of the magnetic pole of this invention; 
     FIG. 16 is a cross-sectional view showing a modified embodiment of FIG. 4; 
     FIG. 17 is a perspective view showing a modified embodiment of FIG. 7; 
     FIG. 18 is a cross-sectional view showing a modified embodiment of FIG. 9; 
     FIG. 19 is a perspective view showing a modified embodiment of FIG. 11; 
     FIG. 20 is a perspective view showing a magnetized condition of the magnetic pole of FIG. 18; 
     FIG. 21 is a perspective view showing a modified embodiment of FIG. 15; 
     FIG. 22 is a perspective view showing a further embodiment of this invention; 
     FIG. 23 is a cross-sectional view showing the embodiment of FIG. 22; and 
     FIG. 24 is a perspective view showing another embodiment of the principal part of FIGS. 22 and 23. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will hereinbelow be given on one embodiment of this invention with reference to FIGS. 3 and 4, in which elements corresponding to those of FIG. 1 are shown by the same reference numerals with their repeated description being omitted. 
     In this invention, an armature 15 is formed in substantially a cross shape as shown in FIG. 3, by way of example. Opposite members 15a and 15c of the armature 15 are respectively wound thereon independently with coils 3a and 3c having the same number of windings and these coils 3a and 3c are connected in series. Similarly, the other opposite members 15b and 15d thereof are also wound thereon independently with the coils 3b and 3d having the same number of windings and these coils 3b and 3d are connected in series. The armature 15 wound thereon with these coils 3a, 3b, 3c and 3d is attached to an N-pole surface of a ring-shaped magnet 16 through the damper 4. A magnetic material may be used as the ring-shaped magnet 16. In this case, the magnet or magnetic material 16 is provided with a bore 16a at its center and magnetized as N-pole at its one end surface and as S pole at its other end surface. Reference numeral 17 denotes a holder consisting of a magnetic material, a magnet or the like. The holder 17 is provided at its center with a projection 17a having a diameter which is smaller than that of the center bore 16a of the ring-shaped magnet 16 and a length which is substantially equal to that of the ring-shaped magnet 16. Thus, the S-pole surface of the ring-shaped magnet 16 is brought into contact with the holder 17 and hence the top end of the projection 17a becomes S pole. Further, as shown in FIG. 4 the pipe 10 for fixing a suspension wire 18 is inserted into the bore 11 formed at the center of the projection 17a of the holder 17 and fixed thereto by the set screw 12. 
     With the above described construction of this invention, the electromotive force generating method will hereinafter be described referring to FIGS. 5A, 5B, 5C and FIG. 6. For the convenience of explanation, an operation of only a single channel of the pickup will be described. FIGS. 5A, 5B and 5C show only the elements relating to the electromotive force generating operation of the pickup. FIG. 5A shows a condition where a stylus of the cantilever 1 is not shifted, and FIGS. 5B and 5C show conditions when the stylus of the cantilever 1 is shifted by angle θ 1  and angle θ 2  from the position shown in FIG. 5A. The coils 3a and 3c are independently wound on the armature 15 as mentioned above. FIG. 6 shows the variation of magnetic flux passing through the coils 3a and 3c of the armature 15 when the armature 15 is inclined as shown in FIGS. 5B and 5C. In FIG. 6, the abscissa indicates inclination angles of the cantilever 1 or inclination angles θ 1  and θ 2  of the armature 15 and the ordinate indicates magnetic fluxes φ 1  and φ 2  passing through the coils 3a and 3c. In this case, the variation of the magnetic fluxes φ 1  and φ 2  is shown by curves 19 and 20, respectively. In other words, when the armature 15 is inclined, the magnetic fluxes φ 1  and φ 2  passing through the armature 15 are increased on the one hand and decreased on the other hand with the center of the armature 15 being made as the borderline. Resultant magnetic flux φ of those φ 1  and φ 2  is quite superior in linearity as shown by a dotted line 21 in FIG. 6. Therefore, if the coils 3a and 3c are connected in series to each other, an electromotive force in proportion to the shifting speed of the stylus or the shifting speed of the armature can be produced as an output of the pickup. 
     In the first embodiment mentioned above, there are provided the ring-shaped magnet 16 and the holder 17 with the projection 17a. Next, another embodiment of the magnetic pole of this invention will be described with reference to FIGS. 7 and 8. FIG. 7 shows a pot-type holder 22 which is formed of a material such as ferrite or the like substantially in pot shape as if the ring-shaped magnet 16 and the holder 17 in the first embodiment are integrally combined. FIG. 8 shows a cross-section of the pot-type holder 22. The outer periphery of the ring portion of the pot-type holer 22 is magnetized as N-pole and the top end of its projection 17a as S-pole, thus the same effect as that of the first embodiment being obtainable. 
     A third embodiment of the magnetic pole is shown in FIG. 9. This embodiment is composed of the combination of the ring-shaped magnet 16, the holder 17 made of magnetic material, and a cylindrical magnet or the projection 17a made of magnetic material having the bore 11 at its center as shown in FIG. 9. Of course, in this case, the end surface of the projection 17a and the end periphery of the ring-shaped magnet 16, both being opposite to the armature 15, are selected to have magnetic poles which are reverse in polarity to each other as shown in FIG. 9. 
     FIG. 10 is a perspective view showing a fourth embodiment of the magnetic pole of this invention, in which there is provided a magnetic material 23 having four legs and the projection 17a having the bore therethrough is disposed inside the magnetic material 23 at its center. 
     In an embodiment of FIG. 11, four rod-like magnets 24a, 24b, 24c and 24d, which are similarly polarized in direction, are planted on a substantially plate-shaped magnetic material 25, and a magnet 24e opposite in polarity to these four rod-like magnets 24a to 24d and having the bore 11 therethrough is planted on the magnetic material 25 at the center among these magnets 24a to 24d. 
     In each of the respective embodiments described above, there is used the pickup to generate an electromotive force based upon the principle shown in FIGS. 5A, 5B and 5C. Meanwhile, as depicted in FIG. 12, only the ring-shaped magnet 16 is used with the aforesaid projection 17a being excluded, and the ring-shaped magnet 16 is made as N-pole at its outer periphery and S-pole at its inner periphery as shown in FIG. 13. With the above arrangement, there can be obtained a pickup which operates based upon the principle shown in FIGS. 14A, 14B and 14C similar to that of FIGS. 5A to 5C. 
     Further, instead of the above mentioned ring-shaped magnet 16, rod-like magnets 26a, 26b, 26c and 26d may be glued to a ring-shaped holder 27 made of a synthetic resin as shown in FIG. 15. 
     FIG. 16 shows another embodiment of the magnetic pole of this invention which is a modification of the embodiment of FIG. 4. As shown in FIG. 16, the projection 17a of the holder 17 is made neutral in polarity, while the ring-shaped magnet 16 is halved in its axial direction to form upper (or right) and lower (or left) semi-cylindrical magnets 16a and 16b which are respectively opposed to the holder 17 with their polarities being reversed to each other. Thus, the magnetic flux φ 1  travels from the N pole of, for example, the upper (or right) semi-cylindrical magnet 16a to the neutral point O of the projection 17a and further the magnetic flux φ 2  travels from the neutral point O to the S pole of the lower (or left) semi-cylindrical magnet 16b thereby to cross the coils 3a and 3c wound on the armature 15. FIG. 17 shows a modified embodiment of FIG. 7, in which the upper (or right) half portion of the pot-type holder 22 is made as N pole and the lower (or left) half portion is made as S pole with the projection 17a being made as neutral. FIG. 18 is a modified embodiment of FIG. 9, in which the ring-shaped magnet 16 is divided into upper half portion and lower half portion which are attached to the holder 17 with opposite polarities to each other, or when being magnetized the upper and lower sides of the ring-shaped magnet 16 are made opposite in polarity to each other, and the projection 17a made of cylindrical magnet or magnetic material and having the bore 11 at its center is made neutral in polarity. 
     Further, FIG. 19 is a modification of the embodiment of FIG. 11, in which the end surfaces of the magnets 24a and 24c and those of the magnets 24b and 24d are respectively reversed in polarity to each other with that of the magnet 24e being made neutral. In an embodiment of FIG. 20, the inner and outer peripheral surfaces of the ring-shaped magnet 16 shown in FIG. 18 are magnetized as illustrated. FIG. 21 is a modified example of FIG. 15 in which the opposing magnets 26a-26d are respectively made reverse in polarity at their opposite surfaces as illustrated. 
     FIGS. 22 and 23 show a further another embodiment of the pickup of this invention. In this embodiment, the magnet 16 is disposed between two magnetic plates 28a and 28b which are substantially parallel to each other. The holder 17 is provided at the lower side between the magnetic plates 28a and 28b and supported at the magnetic plate 28a in a cantilever mode through an aperture 29 bored at the lower part of the magnetic plate 28b which is bent substantially inwardly. With the above arrangement, the vibrating system is inserted through the bore 11 of the holder 17. Further, FIG. 24 shows a modified embodiment of the main part of FIGS. 22 and 23, in which the projection 17a is inserted into the bore of a ring-shaped magnetic material 30 which is magnetized as its one end surface as, for example, S pole by a magnet 31 of N pole provided adjacent tthe ring-shaped magnetic material 30. In this case, the end surface of the projection 17a is made as N pole. 
     It is of course possible to select the shape of the aforesaid armature 15 to be rectangular or any. Besides, in the respective embodiments as described above, the magnetic poles N and S may be made reverse to each other. 
     As the present invention is constructed as mentioned above, any yoke for producing parallel magnetic field as in the prior art is not required and the pickup can be constructed quite compactly in the cantilever support member. Further, since the parallel magnetic field is not formed, the magnetic pole can be made very small in weight such as to be about 1/10 of the prior art one. In addition, as the coils of the armature perform push-pull operation, the magnetic characteristics are superior in linearity and not only the magnetic loss of the armature but also the magnetic distortion can be simultaneously compensated for. 
     While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.