Head drum assembly of video cassette recorder

A head drum assembly of a VCR is disclosed which can prevent Jitter and Wow-flutter of signals while recording and reproducing signals and can additionally supply a lubricant. A bearing housing in which lubricant containing groove is formed is integrally formed with a lower drum. Two journal bearings are mounted on the inner side of the bearing housing and support and lubricate a shaft which drives an upper drum. The lubricant in each of the lubricant containing grooves flows into a clearance between the outer surface of the shaft and the inner surface of each of journal bearings along a path formed by the lubricant containing groove, slits, and the lubricating groove, so that an oil film is formed between the shaft and the inner surface of each of the journal bearings. The lubricant can be additionally supplied through lubricant supplying holes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a head drum assembly, and more 
particularly to a lubricating apparatus for a head drum assembly of a 
video cassette recorder, for supporting and lubricating a shaft of the 
head drum assembly. 
2. Description of the Prior Art 
In general, a video cassette recorder (hereinafter, referred to as a VCR) 
includes a base, a running system installed on the base for drawing out a 
magnetic tape from a cartridge and running the magnetic tape along a 
predetermined path, and a head drum assembly for recording and reproducing 
audio and video signals on and from the magnetic tape. In a head drum 
assembly, high reliability and stability is required, and vibration and 
noise should be controlled as much as possible, in order to clearly record 
and reproduce audio and video signals on and from the magnetic tape. 
If a head drum assembly vibrates severely when it records and reproduces 
audio and video signals on and from the magnetic tape, Jitter and 
Wow-flutter of the signals are generated, thereby deteriorating the screen 
and voice quality of a VCR. In order to settle the above-mentioned 
problems, a head drum assembly is provided with a lubricating apparatus. A 
lubricating apparatus generally uses ball bearings or fluid dynamic 
pressure bearings. 
FIG. 1 shows a conventional head drum assembly of a VCR which uses ball 
bearings. Referring to FIG. 1, a head drum assembly 100 includes a lower 
drum 110, an upper drum 120 for recording and reproducing audio and video 
signals on and from a magnetic tape (not shown), a motor 140 mounted on 
lower drum 110 for generating driving force, a shaft 150 for transferring 
the driving force of motor 140 to upper drum 120, and a lubricating 
apparatus 105 for supporting and lubricating shaft 150. 
Lower drum 110 is fixed to a base (not shown) of the VCR. Motor 140 
includes a stator 141 mounted on lower drum 110 at one side of the lower 
surface of lower drum 110, and a rotor 142 which is radially spaced apart 
from stator 141 and is rotated in magnetic conjunction with stator 141. 
Shaft 150 is connected to rotor 142 through a motor flange 122b so as to 
rotate together with rotor 142. An upper flange 122a is fixed to the upper 
portion of shaft 150. 
Upper drum 120 is fixed to upper flange 122a by screws so as to rotate 
together with shaft 150. Mounted on upper drum 120 are at least two 
magnetic heads 121 for recording and reproducing audio and video signals 
on and from the magnetic tape. Magnetic heads 121 are electrically 
connected to lower drum 110 through the lower surface of upper drum 120 
and a rotary transformer 130 installed to the upper surface of lower drum 
110. Therefore, magnetic heads 121 can be electrically connected to a 
power source or the like while upper drum 120 is rotating. 
The lubricating apparatus 105 includes a bearing housing 160, and upper and 
lower bearings 170a and 170b respectively inserted into the inner side of 
bearing housing 160 at the upper and lower ends of bearing housing 160. 
The outer side of bearing housing 160 is connected to the inner side of 
lower drum 110. An upper receiving recess 162a for receiving upper bearing 
170a is formed at the inner side of bearing housing 160 at the upper end 
of bearing housing 160, and a lower receiving recess 162b for receiving 
lower bearing 170b is formed at the inner side of bearing housing 160 at 
the lower end of bearing housing 160. Each of bearings 170a and 170b 
includes an outer race inserted into each of receiving recesses 162a and 
162b, an inner race into which shaft 150 is inserted, and a plurality of 
balls which are interposed between the inner and outer races, for 
supporting and lubricating shaft 150. The balls are made of steel, and a 
lubricant is supplied in a space between the inner and outer races in 
order to reduce the friction and to cool the bearings. 
Lubricating apparatus 105 supports radial and thrust loads by the weight 
and rotation of shaft 150. When shaft 150, which is inserted into the 
inner race, rotates, the balls make rolling-contact with the inner and 
outer races so as to support and lubricate the loads of shaft 150. 
Nevertheless, in head drum assembly 100, noises and vibrations are 
generated by the rolling contact of the balls. Especially, the vibration 
of the head assembly cause Jitter and Wow-flutter of the information, 
which can critically deteriorate the screen and voice quality of the VCR 
when they are recorded and reproduced on and from the magnetic tape. 
Recently, a lubricating apparatus employing fluid dynamic pressure bearings 
are also used in order to improve the screen and voice quality of a VCR. 
Lubricating apparatuses using fluid dynamic pressure bearings are 
disclosed in U.S. Pat. No. 4,972,283 (issued to Kim on Nov. 20, 1990) and 
U.S. Pat. No. 5,277,499 (issued to Kameyama on Jan. 11, 1994). 
FIG. 2 shows a head drum assembly using the lubricating apparatus of Kim. 
In the head drum assembly 200, a lubricating apparatus 205 includes a 
shaft 250 for transferring the rotating force to an upper drum 220, and a 
bearing housing 260 into which shaft 250 is inserted, bearing housing 260 
having an air flowing hole 265 through which air can communicate between 
the inner and outer sides thereof. 
A plurality of lubricating grooves 251 are formed at the upper and lower 
portions of the outer peripheral surface of shaft 250, and a fluid guiding 
groove 252 is formed at the lower portion of shaft 250 on the outer 
peripheral surface thereof. 
At the upper portion of bearing housing 260 is formed a guiding groove 263 
corresponding to a guide boss 224 in the lower surface of a flange 222a, 
and at the middle portion of bearing housing 260 is formed an air flowing 
groove 264 having a hole 265. At the lower portion of bearing housing 260 
is formed a lubricant containing groove 267 having a plurality of 
lubricating holes 266 and a guide boss 229b corresponding to a guide 
groove 269a having spiral groove 268. Further, a rotor 242 having a magnet 
is fixed, by a screw 290, to a ring collar 255 secured to the lower 
portion of rotary shaft 250. Bearing housing 260 is fixed to the lower 
surface of lower drum 260. 
Shaft 250, flange 222, upper drum 220, ring collar 255, and rotor 242 
(hereinafter, the above parts are referred to as the rotating bodies) are 
all forced upward by the power of the magnet positioned in rotor 242. 
Then, the rotating bodies are moved downward by a downward acting power 
having a value which results from minusing the power of magnet from the 
weight of the rotating bodies. As a result, guide boss 269a of bearing 
housing 260 makes contact with guide groove 269b. As the lubricant 
contained in lubricant containing groove 267 lubricates contacting point 
between guide boss 269b and guide groove 269a, the friction at the 
contacting point decreases. 
According to head drum assembly 200, when shaft 250 is rotated by motor 
240, flanges 222 and upper drum 220 rotate together with shaft 250 and 
magnetic heads 221 attached to upper drum 220 record and reproduce audio 
and video signals on and from the magnetic tape. Nevertheless, in head 
drum assembly 200 of Kim, it is difficult to form grooves on the outer 
peripheral surface. The lubricant can be depleted by its leakage or the 
like, so that the vibrating effect deteriorates and undesired vibrations 
are generated during the rotation of upper drum 220. 
A lubricating apparatus of Kameyama was suggested in order to settle the 
above-mentioned problems. The apparatus of Kameyama includes a shaft, and 
a sleeve having a thrust receiver opposite to an end surface of the shaft, 
into which the shaft is rotatably received. On the inner surface of the 
sleeve near an opening thereof is formed an annular groove. On the outer 
surface of the shaft is formed a plurality of shallow grooves. When the 
shaft rotates, a fluid flows between the inner surface of the sleeve and 
the outer surface of the shaft by following the shallow grooves. Then, the 
fluid flows upward from the center portion of the sleeve at which the 
shaft keeps in contact with the sleeve, so that the friction between the 
shaft and the sleeve decreases. 
Nevertheless, in the lubricating apparatus of Kameyama, since the shaft 
rotates while it is floated from the center portion of the sleeve, the 
upper and lower portions of the shaft can be biased from each other. The 
biasing of the shaft causes vibration of the upper drum of a head drum 
assembly, thereby deteriorating the screen quality of the head drum 
assembly. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a head drum 
assembly of a VCR which can reduce a vibration thereof, and thus record 
and reproduce video and audio signals clearly. 
It is another objects of the present invention to provide a head drum 
assembly of a VCR which can additionally supply a lubricant thereinto. 
In order to achieve the object of the present invention, there is provided 
a head drum assembly comprising: 
a lower drum; 
a motor for generating a driving force, the motor having a stator mounted 
on the lower drum below the lower drum and having a rotor which is 
radially spaced apart from the stator and rotates in magnetic conjunction 
with the stator; 
a shaft connected to the rotor of the motor by a first flange, an upper 
portion of the shaft being inserted into a second flange, the shaft being 
rotated as the rotor rotates; 
an upper drum positioned above the lower drum and fixed to the second 
flange, the upper drum having at least two magnetic heads for recording 
and reproducing signals of the video cassette recorder while the shaft is 
rotating; 
a rotary transformer provided between a lower surface of the upper drum and 
an upper surface of the lower drum, for electrically connecting the 
magnetic heads to the lower drum; 
two journal bearings, into which the shaft is inserted, wherein on an inner 
surface of each are formed two lubricating grooves respectively spaced 
apart from the upper and lower ends of each of the journal bearings, for 
supporting and lubricating the shaft; and 
a bearing housing an outer surface of which is connected to the inner 
surface of the lower drum, and at upper and lower ends of which bearing 
receiving recesses for receiving and supporting the journal bearings are 
respectively formed, wherein lubricant containing grooves are respectively 
formed on inner surfaces of the bearing receiving recesses. 
According to the present invention, a first slit and a second slit are 
respectively formed on the outer and inner surfaces of each of the journal 
bearings along the length of each of the journal bearings and third slits 
are radially formed on the upper and lower surfaces of each of the journal 
bearings, the first and second slits communicating with the lubricant 
containing groove and the lubricating groove respectively, the third slits 
connecting the first and second slits so that the lubricant in each of the 
lubricant containing grooves flows into a clearance between the outer 
surface of the shaft and the inner surface of each of journal bearings 
along the path formed by the lubricant containing groove, the first slit, 
the third slits, the second slit, and the lubricating groove. 
When the shaft rotates, the fluid pressure between the journal bearings and 
the shaft decreases. The lubricant contained in each of the lubricant 
containing grooves flows into a clearance between the shaft and each of 
the journal bearings by a pressure drop, capillary action through the 
slits, and the viscocity of the lubricant. The friction between the shaft 
and the inner surface of each of the journal bearings is decreased by an 
oil film formed between the shaft and the inner surface of each of the 
journal bearings. 
A plurality of lubricating recesses, each of which is defined by a side 
wall, a bottom surface, and an inclined surface, are formed on the upper 
surface of the upper journal bearing. A plurality of protrusions are 
formed between adjacent lubricating recesses so as to support and 
lubricate the second flange. 
The journal bearings are made of a sintering metal of copper or molded with 
Teflon whose friction coefficient is low. Lubricant supplying holes are 
formed in the bearing housing so as to additionally supply the lubricant 
into the lubricant containing grooves. 
In the head drum assembly according to the present invention, the depletion 
of the lubricant can be prevented by additional supplies of the lubricant 
and the structure of the head drum assembly is so simple that the 
manufacturing cost of the assembly can be reduced. Furthermore, the loads 
generated by the shaft and the upper drum can be effectively supported, 
thereby preventing Jitter and Wow-flutter of the signals of the VCR.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, a preferred embodiment of the present invention will be 
described in detail with reference to the accompanying drawings. 
FIG. 3 shows a head drum assembly for a VCR according to a preferred 
embodiment of the present invention. Referring to FIG. 3, a head drum 
assembly 300 comprises a lower drum 310 mounted on a base (not shown) of 
the VCR, an upper drum 320 for recording and reproducing audio and video 
signals on and from a magnetic tape (not shown), a motor 340 mounted on 
lower drum 310 for generating a driving force, a shaft 350 for 
transferring the driving force to upper drum 320, and a lubricating 
apparatus 305 into which shaft 350 is inserted, for supporting and 
lubricating shaft 350. 
Lower drum 310 is fixed to the base of the VCR. Motor 340 includes a stator 
341 mounted on the lower surface of lower drum 310 at one side thereof, 
and a rotor 342 radially spaced apart from stator 341 by a distance for 
rotating by magnetic conjunction with stator 341. Shaft 350 is connected 
to rotor 342 by a first flange 322a so as to rotate together with rotor 
342. Shaft 350 is inserted into a second flange 322b at an upper portion 
of shaft 350. 
Upper drum 320 is fixed to second flange 322b by screws. Mounted on upper 
drum 320 is at least two magnetic heads 321 for recording and reproducing 
the audio and video signals on and from the magnetic tape while shaft 350 
is rotating. Magnetic heads 321 are electrically connected to lower drum 
310 by a rotary transformer 330 which is installed on the lower surface of 
upper drum 320 and the upper surface of lower drum 310. Therefore, 
magnetic heads 321 can maintain electrical connection with a power source 
or the like while upper drum 320 is rotating. 
FIG. 4 is a perspective view for explaining the lubricating apparatus as 
shown in FIG. 3. Referring to FIGS. 3 and 4, lubricating apparatus 305 
comprises a bearing housing 360 connected to the inner side of lower drum 
310, and a journal bearing 30a and 370b into which shaft 350 is inserted. 
Bearing housing 360 is integrally formed with lower drum 310, and at the 
upper and lower ends thereof are formed bearing receiving recesses 362a 
and 362b into which journal bearings 370a and 370b are inserted. The inner 
surface of each of receiving recesses 362a and 362b is formed such that 
each of journal bearings 370a and 370b can be press-fitted therein. Each 
of journal bearings 370a and 370b is axially supported by a supporting 
surface of each of receiving recesses 362a and 362b. On the inner surface 
of each of receiving recesses 362a and 362b is formed a lubricant 
containing groove 365. A lubricant supplying hole 366 extends from the 
outside to the inner surface of each of lubricant containing grooves 365 
is formed in order to supply a lubricant into each of lubricant containing 
grooves 365. 
Journal bearings 370a and 370b are inserted into and fixed to bearing 
housing 360. Lubricating grooves 374 are formed on the inner peripheral 
surface of bearing housing 360. First and second slits 372a and 372b are 
respectively formed on the outer and inner surfaces of each of journal 
bearings 370a and 370b along its length. Third slits 372c are formed on 
the upper and lower ends of each of journal bearing 370a and 370b so that 
each of third slits 372c is connected to first and second slits 372a and 
372b. 
When shaft 350 rotates, the lubricant contained in each of lubricant 
containing grooves 365, flows into a clearance between the outer surface 
of shah 350 and the inner surface of each of journal bearings 370a and 
370b along the path formed by lubricant containing grooves 365, first slit 
372a, third slits 372c, second slit 372b, and lubricating grooves 374. The 
lubricant flowed into the inner surface of journal bearings 370a and 370b 
is supplied to the entire surface of journal bearings 370a and 370b, so 
that an oil film is formed between shaft 350 and the inner surface of 
journal bearings 370a and 370b. The oil film decreases the friction 
between shaft 350 and journal bearings 370a and 370b. 
As shown in FIGS. 4 and 5, lubricating grooves 374 of each of journal 
bearings 370a and 370b are respectively formed spaced apart from the upper 
and lower ends of each of journal bearings 370a and 370b by a distance D1. 
The distance D1 is a distance from the upper (or lower) end of each of 
journal bearings 370a and 370b to the center of the upper (or lower) one 
of lubricting grooves 374, and is equal to or greater than one hundredth 
of the length of each of journal bearings 370a and 370b and equal to or 
smaller than one tenth of the length of each of journal bearings 370a and 
370b so that the effective lubricating area of each of journal bearings 
370a and 370b can be maximized. 
FIG. 6 schematically shows the contacting condition between the upper 
surface of upper journal bearing 370a and the lower surface of a second 
flange 322b. As shown in FIGS. 4 and 6, on the upper surface of upper 
journal bearing 370a in the radial direction are formed a plurality of 
lubricating recesses 375, each of which is defined by a side wall 375a, a 
bottom surface 375c, and an inclined surface 375b, so that the same number 
of protrusions 376 are formed between adjacent lubricating recesses 375. 
Each of protrusions 376 preferably has a shape like a saw-tooth, and 
supports and lubricates second flange 322b. 
Upper third slit 372c is formed on one of the bottom surfaces 375c, and the 
lubricant in lubricant containing grooves 365 flows into lubricating 
grooves 375 through third slits 372c. When shaft 350 and second flange 
322b rotates, since the pressure of the lubricant drops as second flange 
322b rotates, the lubricant in lubricating grooves 375 ascends to the top 
of protrusions 376 along inclined surfaces 375b. As a result, oil films 
are formed between the lower surface of second flange 322b and the top of 
protrusions 376, thereby decreasing the friction between them. The shape 
of protrusions 376 decreases the friction area between upper journal 
bearing 370a and second flange 322b, thereby also decreasing the friction 
between them. 
If dirt is contained in the lubricant, shaft 350 is damaged by scratches or 
the like when rotating, and thus the strength of shaft 350 is decreased. 
Journal bearings 370 are made of a sintering metal of copper or molded 
with Teflon whose friction coefficient is low. The static friction 
coefficient of Teflon against steel is 0.04, which is very small. 
Hereinafter, the operation of above-described head drum assembly according 
to the preferred embodiment will be explained. 
With reference to FIG. 3, an amount of lubricant is supplied into lubricant 
containing grooves 365 through lubricant supplying holes 366, and then 
lubricant supplying holes 366 are closed by screws. 
If electric current is applied to motor 340, rotor 342 and shaft 350 are 
rotated in magnetic conjunction with stator 341. While shaft 350 is 
rotating, magnetic heads 321 attached to upper drum 320 records and 
reproduces the audio and video signals on and from a magnetic tape of the 
VCR. Magnetic heads communicates with other devices through rotary 
transformer 330. 
As shown in FIG. 5, when shaft 350 rotates, the fluid pressure between 
journal bearings 370a and 370b and shaft 350 decreases. The lubricant 
contained in each of lubricant containing grooves 365 flows into a 
clearance between shaft 350 and each of journal bearings 370a and 370b by 
capillary action through first slit 372a, third slits 372c, and second 
slit 372b on each of journal bearings 370a and 370b and a pressure drop. 
The lubricant forms an oil film between shaft 350 and the inner surface of 
each of journal bearings 370a and 370b when it is flowed into a clearance 
therebetween shaft by the viscosity of the lubricant and the rotation of 
shaft 350. Therefore, the friction between shaft 350 and the inner surface 
of each of journal bearings 370a and 370b is decreased. 
As shown in FIG. 6, when upper drum 320 rotates, the lower surface of 
second flange 322b on which head drum 320 is mounted keeps in contact with 
the top surface of upper journal bearing 370a. On the other hand, some of 
the lubricant ascends to the top surface of upper journal bearing 370a 
along inclined surfaces 375b. As an oil film is formed between the lower 
surface of second flange 322b and the top of protrusions 376, and the 
friction between shaft 350 and journal bearings 379a and 370b is 
decreased. Therefore, vibration and noise generated by the rotation of 
shaft 350 can be decreased, and thus signals on and from the tapes can be 
clearly recorded and reproduced and the screen and voice quality of the 
VCR can be increased. 
According to the head drum assembly of the present invention, as 
above-mentioned, vibration and noise can be effectively controlled, and 
the structure of the head drum assembly is simple, so the manufacturing 
cost of the assembly can be reduced. Furthermore, since lubricant 
supplying holes are provided with the assembly, the lubricant can be 
additionally supplied if necessary. 
While the present invention has been particularly shown and described with 
reference to a particular embodiment thereof, it will be understood by 
those skilled in the art that various changes in form and details may be 
effected therein without departing from the spirit and scope of the 
invention as defined by the appended claims.