Rotary head assembly

A rotary head assembly has a first positioning surface and a second positioning surface provided in a rotary yoke. The first positioning surface contacts an end surface of a rotor of a rotary transformer. The second positioning surface contacts an outer peripheral surface of the rotor of the rotary transformer. A rotary yoke is fixed on the rotor by magnetic force by a motor. The rotary yoke is positioned by the first positioning surface in a thrust direction, and by the second positioning surface in a radial direction. Thus, the rotary yoke can be easily and precisely attached.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rotary head assembly used in a VTR, a 
R-DAT and the like. More specifically, the present invention relates to a 
rotary head assembly having a rotor of a motor for rotatably driving a 
rotary drum contained in the rotary drum. 
2. Description of the Background Art 
FIG. 11 is a cross sectional view of a conventional rotary head assembly. 
The rotary head assembly includes a rotary drum 1, a fixed drum 9, a motor 
7 and a rotation shaft 13. The rotation shaft 13 is rotatably held by a 
ball bearing 15. An outer ring of ball bearing 15 is attached to fixed 
drum 9 by shrinkage fitting and adhesion. 
A rotary drum 1 is arranged at a position opposing fixed drum 9. A disk 3 
is attached to rotation shaft 13. Rotary drum 1 is attached to disk 3 by 
means of a fitting screw 2. If rotary drum 1 is directly attached to the 
shaft 13 of rotation, precision of height of a magnetic head 11 and the 
like becomes inferior. For this reason, rotary drum 1 is attached to disk 
3 in order to improve precision in attaching rotary drum 1. Magnetic head 
11 is attached on an end surface of rotary drum 1. Magnetic head 11 is 
rotated to scan a magnetic tape (not shown). 
A rotor 5a of a rotary transformer is attached to disk 3 by adhesion. A 
stator 5b of the rotary transformer is attached to fixed drum 9 by 
adhesion. Rotor 5a and stator 5b of the rotary transformer are opposing to 
each other. A prescribed air gap is provided between rotor 5a and stator 
5b of the rotary transformer. The rotary head assembly transmits and 
receives electric signals to and from magnetic head 11 by means of this 
rotary transformer. This rotary transformer is a flat type one. 
Rotary drum 1 is arranged at one end portion of rotation shaft 13. Motor 7 
is arranged at the other end portion of rotary shaft 13. Rotor 6 of the 
motor is attached to fixed drum 9. The shaft 13 is rotatably driven by 
means of motor 7. Members rotated by the rotation of shaft 13 include 
rotary drum 1, rotor 5a of the rotary transformer, disk 3 and magnetic 
head 11. 
Problems of the rotary head assembly shown in FIG. 11 will be described in 
the following. Since the rotary head assembly has been reduced in size 
recently, rotation shaft 13 has been made thinner. If rotation shaft 13 is 
thin, it is likely to be twisted when rotation shaft 13 is rotatably 
driven by means of motor 7. When rotation shaft 13 is twisted, a jitter is 
generated. The jitter appears as a distortion on a TV screen. 
A rotary head assembly disclosed in Japanese Patent Laying-Open No. 2-9013 
has been proposed to solve this problem. FIG. 12 is a cross sectional view 
of the rotary head assembly disclosed in this Japanese Patent Laying-Open 
No. 2-9013. The rotary head assembly includes a rotary drum 17, a fixed 
drum 29 and a fixed shaft 31. 
Fixed shaft 31 is inserted through ball bearing 41. A disk 43 is attached 
on an outer ring 27 of ball bearing 41. By press fitting the fixed shaft 
31 to a hole portion 45 provided on the fixed drum 29, as shown in FIG. 
13, the fixed shaft 31 is attached to fixed drum 29. 
As shown in FIG. 12, rotary drum 17 is arranged to oppose to fixed drum 29. 
Rotary 17 is attached to disk 43 by means of a fitting screw 30. A head 
base 34 is attached on a side surface of rotary drum 17 by means of a 
fitting screw 36. A head chip 3 is attached at a tip end portion of head 
base 34. Head base 34 and head chip 35 constitute a magnetic head. 
An earth ring 39 is attached to fixed shaft 31. Stator 25 of the motor is 
attached to earth ring 39 by means of a fitting screw 24. A yoke 23 is 
attached to rotary drum 17 by means of a fitting screw 26. A magnet 21 is 
attached to yoke 23. Yoke 23 and magnet 21 constitute a rotor of the 
motor. A rotary yoke 19 which is a metal plate is attached to rotary drum 
17. By means of the rotary yoke 19, a magnetic path is formed between 
magnet 21 and rotary yoke 19. Therefore, magnetic force of magnet 21 is 
effectively applied to stator 25. 
An earthing brush is attached to yoke 23. Earthing brush 37 is in contact 
with earth ring 39. When rotary drum 17 rotates, earthing brush 37 rotates 
around earth ring 39 while contacting earth ring 39. Rotary drum 17 is 
grounded by means of this earthing brush 37. 
A stator 33a of rotary transformer is attached to fixed drum 29. A rotor 
33b of rotary transformer is attached to rotary drum 17. Stator 33a and 
rotor 33b of the rotary transformer are opposing to each other. A 
prescribed air gap is provided between stator 33a and rotor 33b of rotary 
transformer. 
In the rotary head assembly shown in FIG. 12, members which are rotated 
include rotary drum 17, rotary yoke 19, magnet 21, yoke 23, rotor 33b of 
the rotary transformer, head base 34, head chip 35, earthing brush 37, 
ball bearing 41 and disk 43. 
In the rotary head assembly shown in FIG. 12, rotor (yoke 23, magnet 21) of 
the motor for rotatably driving rotary drum driving rotary drum 17 is 
attached to rotary drum 17. Therefore, even if the shaft 31 is thin, the 
fixed shaft 31 is not twisted. 
The problems of the rotary head assembly shown in FIG. 12 will be described 
in the following. 
(1) Processing of disk 43 is carried out by rotating disk 43. As the fixed 
shaft 31 is attached to fixed drum 29, processing of disk 43 becomes 
impossible. Therefore, before attaching fixed shaft 31 onto the fixed drum 
29, disk 43 must be processed. In this case, if the fixed shaft 31 is 
attached inclined on the fixed drum 29, the rotary drum 17 cannot be 
attached but inclined. 
(2) In the rotary head assembly, a flat type rotary transformer is used. 
Since the rotary head assembly is made smaller and smaller, the rotary 
transformer becomes thinner. The rotary transformer is processed by 
grinding. If the rotary transformer is thin, it may possibly warp during 
grinding. If such a rotary transformer is used, the air gap between the 
stator 33a and rotor 33b of the rotary transformer cannot be precisely 
provided. 
(3) In the rotary head assembly, the rotary drum 17 is grounded by the 
contact between earthing brush 37 and earth ring 39 provided on the outer 
ring of fixed shaft 31. Resistance at the contact between earthing brush 
37 and earth ring 39 has effected the precision of rotation of the rotary 
drum 17. 
(4) Since the rotary head assembly is made smaller, thickness of the outer 
periphery of the rotary drum 17 is also made thinner. In order to rotate 
rotary drum 17 with less power consumption, it is preferred to position 
the motor on outermost side. Since the outer periphery of rotary drum 17 
is thin and the motor is positioned on the outer side, magnetic tape is 
affected by the magnetic force of the motor. 
(5) The fixed shaft 31 is attached to fixed drum 29 by press fitting. 
Therefore, it was difficult to accurately provide the air gap between 
rotor 33b and stator 33a of the rotary transformer. 
(6) Rotor 33b of the rotary transformer to rotary drum 17 was done by 
adhesion. Therefore, rotor 33b of the rotary transformer could not be 
changed. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a rotary head apparatus 
having a structure allowing improved precision in assembly. 
Another object of the present invention is to provide a rotary head 
assembly having a structure allowing improved precision in assembly and 
improved precision in rotation of the rotary drum. 
A further object of the present invention is to provide a rotary head 
assembly having a structure allowing improved precision in assembly, and 
in which magnetic tape is not affected by the magnetic force from the 
motor rotatably driving the rotary drum. 
A still further object of the present invention is to provide a rotary head 
assembly having a structure allowing improved precision in assembly and 
easier attachment of rotary yoke. 
A still further object of the present invention is to provide a rotary head 
apparatus having a structure allowing improved precision in assembly and 
exchange of the rotor of the rotary transformer. 
According to one aspect of the present invention the rotary head assembly 
includes: a rotary drum on which a magnetic head is attached; a rotation 
shaft fixedly attached to the rotary drum; a fixed drum for rotatably 
holding the rotation shaft and arranged opposing to the rotary drum; and a 
motor for rotatably driving the rotary drum. The motor includes a stator 
attached to the fixed drum, and a rotor attached on the rotary drum to be 
opposed to the stator. 
According to a second aspect, the rotary head assembly of the present 
invention includes a shielding member for shielding the magnetic tape from 
magnetism from the motor, provided between the magnetic tape and a space 
formed by the rotor and the stator of the motor. 
In accordance with a third aspect, the rotary head assembly of the present 
invention transmits and receives electric signals to and from the rotary 
drum and the fixed drum, and it includes a coaxial type rotary transformer 
provided coaxially with the rotation shaft. The coaxial type rotary 
transformer includes a cylindrical rotor attached to rotary drum, and a 
cylindrical stator attached to a fixed drum arranged to oppose to the 
inner surface of the rotor. In accordance with the third aspect, the 
assembly further includes a pressing surface provided on the outer 
peripheral surface of the rotor of the coaxial type rotary transformer, 
and a pressing member detachably attached on the rotary drum for 
depressing the pressing surface so as to attach the rotor of the coaxial 
type rotary transformer onto the rotary drum. 
According to a fourth aspect, the rotary head assembly of the present 
invention includes a rotary yoke arranged opposing to the stator of the 
motor and arranged to sandwich, together with the rotor of the motor, the 
stator of the motor. The rotary yoke contacts the rotor of the rotary 
transformer and rotates together with the rotor of the rotary transformer. 
The rotary yoke includes a first positioning surface which contacts an end 
surface of the rotor of the rotary transformer for positioning the rotary 
yoke in the thrust direction, and a second positioning surface which 
contacts an outer peripheral surface of the rotor of the rotary 
transformer for positioning the rotary yoke in the radial direction. 
In the rotary head assembly in accordance with the present invention, the 
disk can be rotated by rotating the rotation shaft after the rotation 
shaft is held by the fixed drum. Therefore, even after the rotation shaft 
is held by the fixed drum, the disk can be processed. 
In the rotary head assembly in accordance with the present invention, a 
coaxial type rotary transformer is used. Therefore, even if the rotary 
transformer is made thin, it does not warp. 
In the rotary head assembly in accordance with the present invention, the 
rotary drum is grounded by bringing a terminal into contact with an end 
surface of the rotation shaft. The resistance at the contact portion 
between the terminal and the end surface of the rotation shaft does not 
match effect the precision in rotation of the rotary drum. 
The rotary head assembly in accordance with the present invention shields 
the magnetic tape from magnetism of the motor by means of a shield member. 
Therefore, the magnetic tape is hardly affected by the magnetism of the 
motor. 
Since the rotary yoke is fixed to the rotary drum by the magnetic force of 
the motor in the rotary head assembly in accordance with the present 
invention, the rotary yoke can be easily attached. 
Further, the rotor of the rotary transfer is used for positioning the 
rotary yoke. Since the rotary transformer is processed by grinding, 
precision in processing can be made high. Therefore, use of the rotor of 
the rotary transformer in positioning improves accuracy of the arrangement 
of the rotary yoke. 
In the rotary head assembly in accordance with the present invention, the 
rotor of the rotary transformer is pressed onto the rotary drum by means 
of a pressing member. The pressing member is detachably provided on the 
rotary drum. Therefore, the rotor of the rotary transformer can be 
changed. 
The foregoing and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a cross sectional view of one embodiment of the rotary head 
assembly in accordance with the present invention. The rotary head 
assembly includes a rotary drum 51, a fixed drum 53, a ball bearing 63 and 
a rotation shaft 61. 
Ball bearing 63 rotatably supports the rotation shaft 61. Fixed drum 53 
fixes an outer ring 65 of ball bearing 63. Outer ring 65 is fixed to the 
fixed drum 53 by shrinkage fitting and adhesion. Fixed drum 53 is attached 
to a V base 55. V base 55 is attached on a mechanism chassis 57. An 
earthing brush 59 is attached to mechanism chassis 57. Earthing brush 59 
is in contact with an end surface of rotation shaft 61. 
A disk 82 is attached to rotation shaft 61. Rotary drum is attached to disk 
82. In one embodiment of the rotary head assembly in accordance with the 
present invention, a coaxial type rotary transformer is used. A rotor 79 
of the rotary transformer is attached to rotary drum 51. A stator 81 of 
rotary transformer is attached to fixed drum 53 The rotary transformer 
transmits electric signals to the magnetic head and receives electric 
signals from the magnetic head. The magnetic head 77 is attached on rotary 
drum 51. 
Rotor 75 of the motor includes a yoke 73 and a magnet 71. Rotor 75 of the 
motor is attached to rotary drum 51 by means of a fitting screw 76. A 
rotary yoke 67 is provided at an end surface of rotor 79 of the rotary 
transformer. Rotary yoke 67 is fixed to rotor 79 of the rotary transformer 
by the attraction force from magnet 71. 
Stator 69 of the motor is attached to fixed drum 53 by means of a fitting 
screw 70. Stator 69 of the motor opposes to rotor 75 of the motor. 
Referring to FIG. 1, elements which rotate include rotary drum 51, rotation 
shaft 61, rotary yoke 67, rotor 75 of the motor, magnetic head 77, rotor 
79 of the rotary transformer, and disk 82. 
Outer ring 65 of ball bearing 63 and fixed drum 53 are fixed by shrinkage 
fitting and adhesion. Therefore, compared with the case when they are 
fixed by press fitting, the amount of air gap between rotor 75 of the 
motor and stator 69 of the motor can be accurately adjusted. 
In addition, since this 82 can be processed after ball bearing 63 is fixed 
to fixed drum 53, rotary drum 51 can be attached with high precision. 
Rotor 75 of the motor for rotatably driving rotary drum 51 is fixed to 
rotary drum 51, and therefore torsion can be prevented, and precision in 
rotation can be improved. 
Since the rotary transformer is coaxial type, there is less variation of 
opposing areas in the core compared with a flat type one. Since the 
opposing areas in the core are uniform, the transmission characteristic of 
the rotary transformer is the same in every channel. Therefore, 
characteristic adjustment of recording/reproducing amplifier and the like 
is not necessary. 
In addition, since the rotary transformer is coaxial type, it does not warp 
during processing even if the rotary transformer is thin. 
Earthing brush 59 is in contact with the end surface of rotary shaft 61. 
Therefore, compared with the rotary head assembly shown in FIG. 12, 
precision in rotation of the rotary drum 51 can be improved. 
FIG. 2 is a cross sectional view of a motor provided in one embodiment of 
the rotary head assembly in accordance with the present invention. FIG. 3 
is a plan view of the motor shown in FIG. 2. FIG. 4 is a plan view of a 
stator 69 of the motor shown in FIG. 2. FIG. 5 is a plan view of a shield 
ring 111 supporting stator 69 of the motor shown in FIG. 2. FIG. 6 is a 
cross sectional view of the shield ring 111 shown in FIG. 5 taken from the 
direction of the arrow A. 
As shown in FIG. 2, rotor 75 of the motor is formed by attaching magnet 71 
to yoke 73. By fixing a fitting boss 113 provided on yoke 73 to rotary 
drum 51 shown in FIG. 1 by means of a fitting screw 76, rotor 75 of the 
motor is attached to rotary drum 51. 
As shown in FIG. 2, stator 69 of the motor is attached to shield ring 111. 
Shield ring 111 serves to maintain flatness of rotor 69 of the motor. 
As shown in FIGS. 2 and 4, a projecting portion 121 is provided on stator 
69 of the motor. As shown in FIG. 4, a connecting hole 123 is provided at 
projecting portion 121. Stator 69 of the motor has a ring shape. A 
plurality of driving coils 119 are provided on stator 69 of the motor. 
Projecting portion 121 provides electric connection between driving coils 
119 and connecting pins 117 provided at a lead wiring member 115. 
When connecting hole 123 shown in FIG. 4 is provided at a portion for 
forming driving coil 119 of stator 69 of the motor, the driving coils 119 
positioned at that portion becomes smaller than driving coil 119 
positioned at other portions. Therefore, magnetic flux generated from the 
driving coil 119 at the connection hole becomes smaller than the magnetic 
flux generated from other magnetic coils 119 positioned at other portions. 
The magnetomotive force F is represented as F=B.multidot.I.multidot.1 (B: 
flux density, I.multidot.current, 1.multidot.effective length of coil). 
The driving coil 119 at the connection hole has smaller coil area than 
other coils, that is, shorter effective length of the coil, which results 
in smaller magnetomotive force. If the same magnetomotive force (as 
provided by an example in which all coils have the same size) is to be 
provided, the current must be increased, as apparent from the above 
expression. Consequently, much power is consumed. However, since the 
driving coils 119 have the same size in the present invention, such 
problem does not occur. 
As shown in FIG. 5, a stator fixing portion 131 is provided on shield ring 
111. A rising portion 127 is provided around stator fixing portion 131. 
rising portion 127 is not provided at a portion corresponding to 
projecting portion 121 shown in FIG. 4. A fixed tapped hole 125 is 
provided on shield ring 111. By fitting the screw 70 shown in FIG. 1 into 
tapped hole 125, shield ring 111 is fixed on fixed drum 53. Shield ring 
111 is formed of a magnetic material such as permalloy. 
FIG. 7 is a perspective view showing the state of attachment of stator 69 
of the motor shown in FIG. 4. A step is provided on the outer periphery of 
fixed drum 53, which step serves as a lead portion 135. The lead portion 
135 regulates traveling of magnetic tape. In one embodiment of the rotary 
head assembly in accordance with the present invention, a notched portion 
133 is provided at that portion of the outer peripheral surface of the 
fixed drum 53 at which magnetic tape is not wound, and a lead wiring 
member 115 having a connecting pin 117 attached thereto is fit in notched 
portion 133. 
FIG. 8 is an enlarged sectional view of a motor provided in one embodiment 
of the rotary head assembly in accordance with the present invention. A 
ball bearing 63 rotatably supports a rotation shaft 61. An outer ring 65 
of ball bearing 63 is fixed by a fixed drum 53. A shield ring 111 is 
attached to fixed drum 53 by means of a fitting screw 141. Shield ring 111 
supports stator 69 of the motor. There is rising portion 127 provided on 
shield ring 111 between stator 69 of the motor and fixed drum 53. 
A disk 82 is attached to rotation shaft 61. Rotary drum 51 is attached to 
disk 82. A rotor 79 of a rotary transformer is attached to rotary drum 51. 
A stator 81 of rotary transformer is attached to fixed drum 53. 
Rotor 75 of the motor includes a magnet 71 attached to a yoke 73. By 
fitting a fitting screw 76 into fitting boss 113 provided on yoke 73, the 
rotor 75 of the motor is attached to rotary drum 51. 
Rotary yoke 67 includes a first positioning surface 137 and a second 
positioning surface 139. Positioning of rotary yoke 67 in the thrust 
direction is carried out by first positioning surface 137. Positioning of 
rotary yoke 67 in the radial direction is done by second positioning 
surface 139. 
Since recent rotary head assemblies are made smaller and smaller, thickness 
of the outer peripheral portion of the fixed drum 53 becomes thinner. At 
present, outer peripheral portion of the fixed drum 53 having the 
thickness as thin as about 0.6 mm has been known. Meanwhile, in order to 
increase the number of rotation of the motor with less power, the motor 
should be provided as far away from rotation shaft 61 as possible. If the 
motor is provided far from rotation shaft 61, the distance between 
magnetic tape and the motor becomes shorter, and accordingly, the magnetic 
tape is affected by the magnetic force of the motor. In one embodiment of 
the rotary head assembly in accordance with the present invention, a 
rising portion 127 is provided to entirely surround the gap between the 
rotary yoke 67 and the rotor 75 of the motor. The length of rising portion 
127 along the longitudinal direction of rotation shaft 61 is the same or 
longer than the distance of this gap. 
Therefore, influence of the magnetic force from stator 69 of the motor on 
magnetic tape can be prevented. The effect of magnetic shield can be 
expected if the rising portion 127 has the thickness of 0.1 mm or larger. 
As shown in FIG. 8, in one embodiment of the rotary head assembly in 
accordance with the present invention, rotary yoke 67 is positioned by 
rotor 79 of the rotary transformer. Since the rotary transformer is 
processed by grinding, high precision in processing is possible. Since 
rotor 79 of the rotary transformer is used as a reference for positioning 
rotary yoke 67, rotary yoke 67 can be arranged accurately. In addition, 
since rotary yoke 67 is attached by using attraction force from magnet 71, 
rotary yoke 67 can be easily attached to rotor 79 of the rotary 
transformer. 
FIG. 9 is a cross sectional view showing the state of attachment of the 
rotor of the rotary transformer provided in one embodiment of the rotary 
head assembly in accordance with the present invention. FIG. 10 is a plan 
view showing the state of attachment of the rotor of the rotary 
transformer provided in one embodiment of the rotary head assembly in 
accordance with the present invention. As shown in FIG. 9, rotor 79 of the 
rotary transformer is positioned in the thrust direction by a reference 
surface 143 provided on rotary drum 51. A stop is provide on the outer 
periphery of rotor 79 of the rotary transformer. A ring 145 is fixed by 
adhesive on the outer periphery of the rotor 79 of the rotary transformer. 
Ring 145 is positioned by a suppressing surface 159 of the step provided 
on the outer peripheral surface of rotor 79 of the rotary transformer. 
Rotor 79 of the rotary transformer is attached on rotary drum 51 by 
depressing ring 145 by a leaf spring 147. Leaf spring 147 is attached to 
rotary drum 51 by means of a fitting screw 149. Magnetic head 77 is 
electrically connected to a terminal plate 89. Reference numeral 93 
denotes a screw for fixing magnetic head 77 to rotary drum 51. 
A lead pin 151 is attached to ring 145. A connecting portion 153 between 
one end portion of lead pin 151 and wiring of rotor 179 of the rotary 
transformer is in a through hole 157 provided in rotary drum 51. The other 
end of lead pin 151 is electrically connected to terminal plate 89. 
As shown in FIGS. 9 and 10, rotor 79 of the rotary transformer is attached 
to rotary drum 51 by means of leaf spring 147 in one embodiment of the 
rotary head assembly in accordance with the present invention. Therefore, 
rotor 79 of the rotary transformer can be exchanged. Ring 145 is provided 
between rotor 79 of the rotary transformer and leaf spring 147 from the 
following reason. Namely, rotor 79 of the rotary transformer is formed of 
ferrite, which is a brittle material. Therefore, if rotor 79 of the rotary 
transformer is directly depressed by leaf spring 147, rotor 79 of the 
rotary transformer may be damaged. Ring 145 should preferably be made of a 
soft material such as resin. 
As shown in FIG. 9, in one embodiment of the rotary head apparatus in 
accordance with the present invention, one end portion of lead pin 151 is 
connected to rotor 79 of the rotary transformer through the through hole 
157 provided in rotary drum 51. Therefore, soldering of the connecting 
portion 153 is easy. The other end portion of lead pin 151 is adapted to 
contact terminal plate 190 when rotary 79 of the rotary transformer is 
attached to rotary drum 51. If there is no possibility of rotor 79 of the 
rotary transformer being damaged when rotor 79 of the rotary transformer 
is directly depressed by leaf spring 147, ring 145 is not necessary. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.