Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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sackground of the Invention
This invention relates to a magne-tic recording and
reproducing device, and more particularly to a maglletic
recording and reproducing device for recording video signals
intermittently on a magnetic -tape by rotary heads at various
tape moving speeds~
Usually, in a magnetic recording and reproducing
device for recording a video signal, which is taken ou-t at
every n fields (n being an interger), intermittently on a
magnetic tape moving at a speed of l/n of the standard speed, in
order -to provide Eor the conventional tape moving speed and a
low -tape moving speed, separate motors for the different speeds
are used with one motor provided for the conventional speed
and the other for the low speed. With this arrangement
it is required to provide a number of mo-tors corresponding to
the number of tape moving speeds and this is undesirable
because of the high cost and the complex mechanism needed for
switching the driving operation among the different motors.
Alterna-tively, a pulse motor can be used for moving
the magnetic tape and the tape moving speed can be changed by
changing the pulse frequency applied to -the pulse motor.
However, because the pulse motor rotates intermittently,
especially in the case when the frequency of the pulses applied
to the motor is low, there is caused a large deviation in the
tape moving speed and this makes it difficult to hear an audio
signal recorded continuously at the edge of the tape owing
to wow and flutl:er of -the tape. Moreover, in the case of a
high frequency of the pulse being applied -to the motor, there
is a drawback in that a large amount of power is required to
drive the motor well.
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Summary of -the lnvention
There-fore, an object of the present invention is to
provide a novel and improved magne-tic recording and reproducing
device in which a video signal is recorded intermit-tently Oll a
magne-tic tape which is moved by a novel driving system at
various speeds.
Another object o~ the present invention is to
provide such a novel tape driving system which can be operated
at a low power.
A further object of the present inven-tion is -to
provide such a novel tape driving system which has improved
eharaeteristics with respect to wow and flutter of an audio
signal recorcled continuously on a magnetie tape.
A ~urther objee-t of the present invention is to
provide a novel eireuit eonfiguration for such a novel tape
driving system whieh overcomes the eonventional drawbacks as
deseribed above..
In aehieving these objeets, the present invention
employs a brushless motor having a uniform rotation obtained
by multi-pole magnetization as the motor for moving the
magnetie tape, and the motor is driven as a eonventional DC
; brushless motor within a eertain range of values of the tape
moving speed and is driven foreedly by adclitional pulses at
a very low tape moving speed.
The foregoing objeets are aehieved by a magnetie
reeording and reprodueing deviee aceording to the present
invention, whieh eomprises: a brushless DC motor for moving
said magnetie tape at various tape moving speeds whieh motor
has a rotor, a stator eore having main windings wound thereon
faeing to said :rotor, and a position deteeting means for
deteeting the rotational posltion of said rotor; currellt
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supply means for supplying cirren-t to said main windiny so as
-to drive said motor; additional input means which is operated
by an additional pulse applied thereto, said position detecting
means and said additional input means being coupled to said
current supply means so as to supply current thereto; and
selecting means for selecting between said position detecting
means and said additional input means so that said mo-tor is
driven by said position detecting means for tape speeds in a
first tape moving speed range of said magnetic tape where
playback of the audio signal can be carried out in a prac-tical
way and driven by said additional input means for tape speeds
in a second tape moving speed range lower than said first range.
The foregoing objects are achieved by a tape driving
system for a magnetic recording and reporducing device in which
a video signal is recorded intermittently by a rotary magnetic
head and an audio signal is recorded continuously on a magnetic
tape, respectively, said system comprising: a brushless DC
motor for moving said magnetic tape at various tape moving
speeds and having a rotor, a stator core having main windings
wound thereon and opposed to said rotor, and a position detec-
ting means for detecting the rotational position of said rotor;
current supply means for supplying current to sald main winding
so as to drive said motor; and additional input means which is
operated by an additional pulse applied thereto; said posi-tion
detecting means and said additional input means being coupled
to said current supply means for supplying current thereto, and
selecting means coupled to said position detecting means and
said.additlonal input means for selecting the output of said
position detect~ng means to be supplied to said current supply
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means for driving said mo-tor by sai,d posi-tion detecting means
for speeds in a firs-t range of tape moving speeds where play-
back of the audio signal can be carried out in a practical way
and for selecting the output of said additional input means
to be supplied to said current supply means for driving said
motor by said additional input :means for speeds in a second
range of tape moving speeds which is lower than said first range.
The foregoing objects are further achieved by a tape
driving system according to the above, wherein said additional
input means comprises means for producing an output pulse and
said current supply means includes an integrating circuit for
slowing the rise time and fall time of an output pulse supplied
thereto from said additional input means; or by a tape driving
system according to the above, wherein said position detecting
means comprises a current switching transistor, and said current
supply means includes a voltage exchanging means for changing
the base voltage of said current switching transistor to a
reverse bias to the emitter thereof for cutting off the current
supply from said position detecting means to said current supply
- means.
The foregoing objects are still further achieved by a
tape driving system according to the. above, wherein said addi-
tional input means includes-a three-phase pulse generator com-
prising: a 1~3 divider composed of firs-t and second J-K flip-
flop circuits, the T-input terminals of said first and second
J-K circuits being connected in common, the Q-output terminal
of said first J-K flip-flop circuit being connected to the J-
input terminal of said second J-K flip-flop circuit, and the Q-
output terminal of said second flip-flop circuit being connected
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to the J-input -terminal of said first J-K flip-flop circuit;
a first T flip-flop circuit having -the T-input terminal connec-
ted to said Q-output kerminal of said second J-K flip-flop cir-
cuit; a first and a second differentiation circuit; a second T
flip-flop circuit having the T-:input terminal connected to said
Q-output terminal of said second J-K flip-flop circuit and a
reset terminal connected to the Q-output terminal of said firs-t
T flip-flop circuit through said first differentiation circuit;
: and a third T flip-flop circuit having the T-input terminal
connected to the Q-output terminal of said first J-K flip-flop
circuit and a reset terminal connected to -the Q-output terminal
.- of said second T flip-flop circuit through said second differ-
entiation circuit; whereby when an input signal having a fre-
quency lower than the field frequency of the video signal is
applied to said common T-terminals of said first and second J-K
flip-flop circuits, output pulses having a phase different from
each other by 3~ radian are provided at said Q-output terminals
of said first, second and third T flip-flop circuits, respec-
~: tively; or by a tape driving system according to -the above, fur-
ther comprising a rotation speed detecting means associated with
siad motor for detecting the rotational speed of said motor, a
reference signal generating means for generating a reference
signal having a frequencyfrom as small as l/n through a frequency
the same as and up to n times the frequency of the vertical syn-
chronizing signal.of the video signal, n being an integer, and
: phase detecting means to which said rota-tion speed detecting
means and said reference signal generating means are connected
and which is con-ected `o said motor for detecting a phase
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diEference between -the signals from sa:id reference signal yen-
erating means and from said ro-tation speed detectiny means,
said reference signal generator further being coupled -to said
additional input means, whereby said motor is ro-tated synchro-
nously by said reference signal from said reference signal gen-
erating means by controlling the curren-t flowing to said position
detecting means by said phase detecting means for said firs-t
range of tape moving speeds, and by applying said reEerence
signal to said additional input means for said second range of
tape moving speeds; or by a tape driving system according to
the above, further comprising frequency dividing means coupled
between said rotation speed de-tecting means and said additional
input means Eor dividing the frequency of the signal from said
rotation speed detecting means, whereby the rotational speed of
said motor is changed by using the difference outputs of said
frequency dividing means.
Brief Description of the Drawings
These and other objects and the fea-tures of the pre-
sent invention will be apparent from consideration of the follow-
ing description of a preferred embodiment toge-ther with the
- accompanying drawings in which:
Fig. 1 is a block diagram of an embodiment of a magne-
tic recording device according to the present invention;
Fig. 2 is a cross sectional view of a capstan motor
used for the device of Fig. l;
Fig. 3 is a circuit diagram of a driving circuit for
the capstan motor of Fig. 2;
,~ Fig. 4 is a circuit diagram of a three-phase pulse
generator for providing pulses to the driving circuit of Fig.
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Figs. 5A-5I are diagrams of waveforms of pulses for
explaining the operation of the pulse generator of Fig. 4.
Detailed Description of a Preferred Embodiment
In a magnetic record:ing and reproducing device
according to the present invention, a brushless DC motor is
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used as a capstan motor for moving a magne-tic -tape, and in
order to change the tape moving speed correctly, the speed of
rotation of -the motor is changed by controlling the rotation
phase -thereof. However, it is difficult to rotate a brushless
DC motor correctly at a very low speed range as described in
the following.
- That is, the amount of load and the amount of change
of load applied -to the magnetic tape moving motor are nearly
constant, respectively, regardless of the tape moving speed.
Therefore, the ratio of the change of the speed of rotation
with respect to the load should be constant regardless of the
speed of rotation of the motor. Accordingly, in the case of
a very low speed of rotation of the motor, the ratio of the
change of the speed of rotation relative to change of the load
should be made very small.
In controlling the speed of rotation of a motor,
lowering the ratio of the change of the speed of rotation
relative to the change of the load requires an increase in the
gain of the speed control system. Such an increase of the
; 20 gain of the speed control system results in a shift of the
frequency response characteristic of the speed control system
including the motor to a high frequency in proportion to that
gain. Therefore, in order to rotate the motor in a stable
manner, it is necessary that the speed con-trol system including
the motor have no phase delay up to a high frequency range.
On the other hand, the motor speed detecting
frequency from a rotation speed detector forming part of the
motor, which is essential for controlling the speed of rota-
tion of the mot:or, is proportional to the speed of rotation of
the motor. Therefore, when considering the change in the ratio
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of -the speed of rotation relative to a load applied -to -the
motor, there is naturally a limi-t for rotating the motor stably
at a very low speed, and -this is true even when rotating the
motor by controlling the rota-tion phase of the motor. For the
above reason, according -to the invention, a-t a very low speed
of rotation of the tape moving motor, the conventional brush-
-less DC mo-tor is driven forcedly by additional pulses in order
to prevent a change of the tape moving speed due to a change
of the load on the motor.
The range of the tape moving speeds at which the
motor is driven by additional pulses is determined as follows
taking into consideration the wow and f lutter of the audio
signal and the equal interval of magnetic tract.s in-termitten-tly
formed by the rotar.y heads. That is, for recording the video
signal, the range of tape moving speeds is lower than the tape
moving speed at which the audio signal continuously recorded
at the edge portion of the magnetic tape can be processed
practically. In order to form the magnetic tracks at equal
intervals, the tape speed is set in a range where the additional
pulses for driving the motor do not occur during a time when
one magnetic track is being formed by a rotary head rotating
synchronously with the frame frequency of the video signal,
that is in a range of the tape moving speeds corresponding to
the frequency of the additional pulses which is less than the
- frame frequency (30 Hz). At this Iow speed range, although
: the audio signal is not recorded, the video signal can be
recorded for a very long time.
; When an additional pulse is applied to the motor, the ,;
motor responds to that pulse and rotates up to the next stable
polnt. When this pulse is applied during a period when a
magnetic track is formed, the formed track has a staircase
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shape and the lineari-ty of the magnetic -track is degraded.
Further, when the number of additional pulses applied to the
motor during each period for one magnetic track is different,
although the average tape moving speed over a lon~ period of
-time is not changed, -the intervals between the adjacent rnagnetic
tracks becomes unequal. In orde:r to prevent such a si-tuation,
-the frequency of -the additional pulses to be applied to -thc motor
is set to be lower than 30 ~z and further -to be synchronous
with the rotary head. In this case, the power required for
driving the motor rotated by the additional pulses of such a
low frequency will be small because the speed of rotation is
very low.
Now, it will be assumed that the presen-t invention
is applied to a standard I-type magnetic recordiny and
reproducing device using two rotary magnetic heads. In such
a standard video tape recorder, the conventional magnetic tape
mo~ing speed is set to be 19.05 cm/sec (EIAJ Standard, Electric
Industry Association of Japan). The magnetic tape moving
speed for recording the video signal intermittently is arranged,
20 for example, to about 2.~ cm, 1.2 cm/sec, 0.6 cm/sec and
0.3 cm/sec which is 1/8, 1/16, 1/32 and 1/64 of the above
mentioned conventional speed of 19.05 cm/sec, respectively.
On the other hand, the wave length of the audio signal, which
is recorded continuously on the track at the edge portion of
the tape, for stable playback is in a range of ~ to 5 micron.
Considering the practical frequency band of the audio signal,
the tape moving speed at which the audio signal can be stably
processed is in a range higher than about 1.2 cm/sec : :
(corresponding to 1/16 of the usual speed) among the above
described speeds.
Accordingly, in the present invention, in a range of
the tape moving speed higher than 1.2 cm/sec, the motor is
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used as a co~ventiollal DC mo~or the rotation phase of whicll is
controlled by means of a reference siynal, so as to improve
the wow and Elut-ter characteristics of the audio signal, -to
reduce the amount of power required for driving the motor and
to maintain the correct moving speed of the magnetic tape.
In the range where the tape moving speed is lower than 1.2
_ cm/sec, the above reference signal is used as an additional
pulse for driving the motor, with such a control that the
additional pulse is not applied to the motor while a magnetic
track is being formed by the rotary magnetic head and tha-t the
interval between the adjacent tracks becomes equal, so as to
maintain the correct moving speed of the magnetic tape.
An embodiment of the invention will be described in
more detail in the following with reference to the drawings.
In the block diagram of Fig. 1, a video signal applied to an
input terminal designated by reference numeral 1 is amplified
by an amplifier ~ and applied to a frequency modulator 3.
The output signal of the frequency modulator 3 is gated for
a time slightly longcr than one field at a gate circuit ~ and
applied to a recording amplifier 5. The signal amplified by
the amplifier 5 is recorded on the magnetic tape 7 by a magnetic
head (not shown) mounted on a rotary head assembly 6.
The video signal at the input terminal 1 is also
applied to a vertical synchronizing signal separating circuit
g where the vertical synchronizing signal is separated -from
the video signal. The separated vertical synchronizing signal
is subjected to wave shaplng by a wave-shaping circuit 9 and
applied to a phase comparator 10. On the other hand, a rotation
phase detector 11 associated with the rotary head assembly 6
3-ne ates one pulse for each rotation Oe the rotary head
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assembly ~, and tllis pulse is applied -to the ph~se comp~lrator
10 after ~ein~ sub~ected to wave shaping by a wave-sll~ping
circuit 12. Thus, -the phase clifEerence between the rotatlon
phase of the rotary head assembly 6 and the vertical synchro-
nizing signal of the video signal applied to the input terminal
1 is detected.
The rotary head assemb:ly 6 is rotated by a motor 13
mounted at the lower portion thereof. A rotation speed
detector 14, which is mounted under the motor 13, generates a
signal having a frequency corresponding to the speed of
rotation of the motor 13, and that signal is amplified by an
amplifier 15 and applied to a speed detecting circuit 16,
which converts the frequency corresponding to the rotation
speed of the motor 13 into a voltage. The output of the phase
comparator 10 and the ou-tput of the speed detecting circuit
16 are applied to an adder 17, and the output signal thereof
is applied to a motor driver 18, which provides the driving
power to the motor 13. Accordingly, the rotary head assembly
is rotated synchronously with the vertical synchronizing
~; 20 signal of the video signal applied to the input terminal 1.
The output of the wave-shaping circuit 12 is also
applied to a first gate signal divider 19, the output of
which is applied to a second gate signal divider 20. In
turn, the output of the divider 20 is applied to a third
gate signal divider 21, and the output of the latter is
applied to a fourth gate signal divider 22. Each of these
outputs of the dividers 19, 20, 21 and 22 is also applied to
a manually set selection circuit 23, which selects an output
depending on the tape speed, which is then applied to a gate
pulse generator 24. The gate pulse generator 24 is connected
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-to the ga-te circuit ~ and determines the yating -time -thereof.
The frequency dividing ratios of the first to the fourth
dividers 19, 20, 21 and 22 are decided according to the time
for recording the video signal intermit-tently on the tape 7,
and also -they must correspond to reduc-tion ratio of a capstan
motor 25 described hereinafter.
The magne-tic tape 7 is moved by the capstan mo-tor
25, and a frequency generator 26 for generating a frequency
corresponding to the speed of rotation of the motor 25 is
mounted on -the mo-tor 25. The output of the generator 26 is
amplified by a motor signal amplifier 27, and the output thereof
is applied to a firs-t motor signal divider 28 for changing the
speed of rotation of the capstan motor 25. In turn, the output
of the first divider 28 is applied to a second motor signal
divider 29. The output of -the amplifier 27 and each o~ -the
outputs of these dividers 28 and 29 is also applied to a
selection circuit 30. The selection circuit selects one of the
outputs of the dividers and the output of the selection circuit
30 is applied to a bi-stable multivibrator 31. The first
output of the bi-stable multivibrator 31 triggers a squa~e
wave generator 32, and the second output thereof is applied to
a sampling pulse generator 33. The pulse from the sampling pulse
'~ generator 33 is applied to a sample holding circuit 34 for
sampling the square wave from the square wave generator 32.
; According to the configuration described above, when the speed
of rotation o~ the capstan motor 25 changes, the frequency of
the frequency generator 26 changes, and thus the period of the
bi-stable multivibrator 32 changes and then there is provided a
voltage change corresponding to the above change of the period
at the sample holding circuit 34.
On the other hand, the second output of the bi-
stable multivibrator 31 lS also applied to a multivibrator
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signal divider 35. The dividing ratio o~ -the divider 35 is
set so that the output frequency thereof becomes the s~me as
or n times or l/n of the frequency of the vertical synchro~
nizing signal of -the video signal (n being an interger).
The output of the divider 35 and the output of the wave-
shaping circuit 9 are applied to a phase comparator 36, where
_ the rotation phase of the capstan motor 25 is compared with
-the phase of the vertical synchronizing signal of the video
signal applied to the input terminal 1. The phase error voltage
from the phase comparator 36 is applied to an adder 38 through
a phase compensating circui-t 37. On the other hand, the speed
error signal from the sample holding circuit 34 is also applied
to the adder 38. The output of the adder 38 is applied to a
capstan motor driving circuit 39 which is described in detail
hereinafter, and power for rotating the motor 25 is provided
therefrom to the motor 25.
In order to rotate the capstan mo-tor 25 by the
additional pulse as described hereinbefore, the output of the
wave-shaping circuit 9 is applied to a shaped wave signal
divider 40 and a selection circuit 41. The selection circuit
41 selects one of these inputs thereto and the output signal
of the selection circuit 41 is applied to a pulse generator 42,
and the output o the latter is applied to the capstan motor
driving circuit 39. The selection circuits 23, 30 and 41 are
manually set in conjunction with each other depending on the
tape speed. The details of the capstan motor driving circuit
39 and the pulse generator 42 are described hereinafter.
Because the o-ther blocks shown in Fig. 1 represent conventional
circuits well known to those skilled in the art, a detailed
description oE them is omitted.
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Fi~. 2 is a cross sectional view of the capstan
mo-tor 25, in which a stator of a brushless mo-tor comprises
a s-tator core 44 moun-ted on a housing 43 and a main winding
45 wound on the stator core 44 in three phases. A ring magnet
47, which is magnetized to have 16 poles, is mounted on a
rotor 48 so that the inner magnet:ic pole surfaces face the
_stator core 44. The rotor 48 is attached to a boss 49 on sha~t
46 which is rotatably mounted in the housing 43 on bearinys
50a and 50b at the opposite ends of the boss 49.
On the inside of the stator core 44, there is
provided a posi-tion detec-ting stator 51 having three pairs
of projections. Facing the position detecting stator 51,
a position detecting ro-tor 52 for indicating the rotational
position of the rotor 48 is attached to the boss 49. A group
of primary coils 53a, 53b and 53c (generally indicated by
numeral 53) and a group of secondary coils 54a, 54b and 54c
(generally indicated by numeral 54) are wound on-the posi-tion
detecting stator 51. In Fig. 2, these coils are shown at
the same position. On the other hand, at the outer periphery
of the position detecting rotor 52, there are provided
projections for changing -the electro-magnetic coupling between
paired primary and secondary coils (53a and 54a, 53b and 54b,
53c and 54c). The number of these projec-tions is small,
being half the number of the poles of the magnet 47.
The driving circuit 39 for rotating the capstan
motor 25 ls shown in Fig. 3, in whlch when the necessary
voltages are applied to terminals 59 and 60 and an oscilla-tor
55 is operated, an AC signal therefrom is supplied to the group
of the primary coils 53a, 53b and 53c and transmitted to
one of the secondary colls 54a, 54b and 54c through the
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position de-tecting rotor 52. When the position detecting
rotor 52 is in a posi-tlon where an electro-magnetic coupling
is produced between -the primary coil 53a and the secondary coil
54a close thereto, a larger AC signal than those induced in
the other secondary coils 54b and 54c is transmit-ted to the
secondary coil 54a, and that AC signal is converted into a DC
~signal through a rectifying and smoo-thing circuit 56a and
applied to the base of a current switching transistor 57a.
Therefore, only the transistor 57a becomes conduc-tive, and
a base current is supplied to an output transistor 58a and
eurrent flows to the main winding 45a. When current flows to
the main winding 45a as described above, the rotor 48 and the
position detecting rotor 52 rotate aceording to attraction and
repulsion caused by that current and the magnet 47. Then, -the
position detecting rotor 52 comes to a position where an
electro-magnetie coupling is produced between the primary coil
53b and the secondary coil 54b close thereto, and similarly
to the above operation, current flows to the main winding 45b.
By this operation according to rotation of the rotor 48, the
20 main windings 45a, 45b and 45c to which current flows are
energized in turn and the rotor 48 rotates continuously.
In the above description it has been stated that
necessary voltages are applied to a power source terminal 59
and a control input terminal 60. The control input terminal 60
is connected to the adder 38 shown in Fig. 1. Rectifying and
smoothing cireuits 56a, 56b and 56c corresponding to the
secondary coils 54a, 54b and 54c, respee-tively are provided
with neeessary bias voltage by bias resistors 61 and 62. A
; bypass capacitor 63 is conneeted in parallel with the bias
~ 30 resistor 62. The eurrent switching transistors 57a, 57b and
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57c are connected in common at thelr emit-ters to a constan-t
current -transistor 64 so as to hold the other -two transistors
in the cut off state when one transis-tor is in a saturation
sta-te. The currents flowing through the output transistors
58a, 58b and 58c are provided out in a form of voltage by
emitter resistors 65a, 65b and 65c. Feedback resistors 66a,
_ 66b and 66c are also connected -to the respec-tive emitters of
the output transis-tors 58a, 58b and 58c in order to decrease
the deviation of the current amplification factor of these
transistors and to determine the transfer conductance of the
capstan motor driving circuit, i.e. the ratio of the change of
current flowing in the main windings 45a, 45b and 45c relative
to the change of voltage applied to the control input terminal
60, by the value of the resistor, and these resistors are
connected to the emitter of a control transistor 68 through a
resistor 67.
Now, referring to Fig. 2 again, the frequency
generator 26 is mounted on the capstan motor 25 so as to
generate a frequency proportional to the speed of rotation
of the motor, as described hereinbefore. A gear 70 is mounted
on the rotating shaft 46 on a boss 69, and an angle bar 73
is attached to the housing 43. In order to provide an AC
` signal corresponding to the number of the gear teeth, a
magnetic head 71 and a ring magnet 72 are mounted on the
angle bar 73. By this structure, the speed of rotation oE
the capstan motor 25 is detected, and it is rotated continuously
under control of the electric circuit 39. Because the ring
magnet 47 is magnetized with 16 poles and the position
detectiny roto:r 52 has 8 projections, as described hereinbefore,
30 current flows 8 times to each of the main windings 45a, 45b
and 45c during one rotation of the capstan motor 25.
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In Fig. 3, capacitors 74a, 74b and 7~c are connected
in parallel to -the main windings 45a, 45b and 45c, respectively
so as -to prevent spike voltages. For stopping opera-tion of
the continuous rotation of the capstan motor 25, there is
provided a transistor 75 and the collector and emitter thereof
are connected across the bias resistor 61. When the -terminal
-76 is grounded, the transistor 75 is saturated and so the base
of the current switching transistors 57a, 57b and 57c are given
a reverse bias to the emitter. Then, current does no-t flow
to the main windings 45a, 45b and 45c.
Now there will be described the case o~ ro-tating the
capstan motor by the additional pulse. In thi.s case, the
terminal 76 is grounded and input -terminals 77a, 77b and 77c
are connected to the pulse generator 42 which is described in
detail hereinafter. The input terminals 77a, 77b and 77c
are connected to current amplifying transistors 79a, 79b
; and 79c through integrating circuits 78a, 78b and 78c,
respectively, and the emitter of each of these transistors is
connected to -the base of the respective output transistors 58a,
58b and 58c. In order to prohibit the driving of the capstan
motor 25 by the additional pulse, there are provided diodes
80a, 80b and 80c connected to the respective integrating
circuits 78a, 78b and 78c and a transistor 81. When a terminal
82 connected to the base of the transistor 81 is connected to
the power source terminal 59, the transistor 81 is saturated
- and so the current amplifying transistors 79a, 79b and 79c
are placed in a cut off state. The situation when the capstan
motor ~5 is rotated by the additional pulse is basically the -
same as the case of a conventional pulse motor, and in the
present invention as a method of exciting the main windings
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45a, 45b and 45c, 1-2 phase excitation :is employed taking into
consider~tion the step number of the capstan motor 25 and
damping of rotation when being clriven by the additional pulse.
In addition, the state of rotation of -the capstan motox 25
can be changed by connecting the terminals 76 and 82 in
common to the power source terminal 59 or to ground.
Next, there will be described what takes place when
pulses are applied to the inpu-t terminals 77a, 77b and 77c. ~s
described hereinbefore, the main windings 45a, ~5b and 45c are
wound in three phases, and thus -the pulses to be applied to the
input terminals 77a, 77b and 77c should have phases which are
different fro~ each other by ~ radian. The pulse generator 42
generates such a three phase pulse, and an embodiment of this
circuit for use in the invention and the wave-shapes of the
signals therein are shown in Figs. 4 and 5, respectively.
The pulse generator 42 comprises five J-K flip-flop circuits
(hereinafter abbreviated as J-K-FF) 83 to 87.
When a pulse signal A as shown in Fig. 5A is applied
to an input 88 in E'ig. 4 which is connected to the selection
circuit 41 in Fig. 1, there are provided the following output
signals to J-K FF 83 and 84 which form a 1/3 divider, i.e.
pulse signals B, C and D for the Q-output of J-K-FF 84, the
Q-output of J-K FF 84 and the Q-output of J-K FF 83, as shown
in Figs. 5B, 5C and 5D, respectively. When -these pulse signals
B, C and D are applied to each input T of J-K-FF 85, 86 and
87, pulse signa:L E as shown in Fig. 5E is provided at tile
Q-output of J-K FF 85. By applying the pulse signal E to a
reset terminal E~ of J-K-FF 86 through a capacitor 89 to pxovide
a wave-shape F as shown in Fig. 5F, pulse signal G as shown
in Fig. 5G i5 provided at the Q-output of J-K FF 86. Further,
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by applylng -this pulse signal G to a reset terminal R of J-K-FF
87 through a capac:itor 87 to provide a waveshape H as shown in
Fig. SH, pulse signal I as shown in Fig. 5I i5 provided at
the Q-output of J-K-FF 87. These output pulse siynals from
J-K-FF 85, 87 and 86 are applied to the input terminals 77a,
77b and 77c in Fig. 3 through terminals 91a, 91b and 97c,
-respectively. As can be understood from the waveshapes of the
pulse signals E, I and G in Figs. 5E, 5I and 5G, the pulse
signal E at the terminal 91a, the pulse signal I a-t -the terminal
91b and the pulse signal G at -the terminal 91c have phases
different from each other by ~ radian. When the pulse
signals each having a phase different from the ot~er by -~
radian are applied to the input terminals 77a, 77b and 77c,
current corresponding to the amplitude of tilese pulse signals
flows to the main windings 45a, 45b and 45c, respectively.
Because the main windings 45a, 45b and 45c are excited by a
1-2 phase excitation method, as described hereinbefore, the
capstan motor 25 rotates one rotation when 48 pulses are applied
to the pulse generator 42.
The integrating circuits 78a, 78b and 78c coupled
between the input terminals 77a, 77b and 77c and the bases of
the current amplifying transistors 79a, 79b and 79c, respectively
are provided for slowing the rise time and fall time of the
pulses of the signals applied to the input terminals 77a, 77b
and 77c, for the following reason. In the case of the usual
continuous rotation of the capstan motor 25, there is caused
a back electro~otive force proportional to the rotation
;~ speed of the capstan motor 25 at the main wlndings 45a, 45b
and 45c. This is an AC voltage, the zero potential of which
is the DC voltage applied to the power source terminaI 59.
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On -the other hand, the pulses of the signals applied to the
input terminals 77a, 77b and 77c have a shor-t rise -time and
fall time. When -these pulses are directly applied -to -the
current amplifying transistors 79a, 79b and 79c, because the
impedance of the main windings 45a, 45b and 45c for the rise
and fall portions of these pulses is mainly an inductance
component, a very high voltage is induced at the ma:in windings
45a, 45b and 45c and the output transistors 58a, 58b and 58c
could be burned out by this induced voltage. If a diode is
connected between the collector of the output transistors 58a,
58b and 58c and the power source terminal 59 in order to
protect these output transistors against the above described
induced vol-tage, the back electromotive Eorce described above
is applied to this diode and current flows there-through, and
so the capstan motor 25 cannot rotate continuously. Therefore,
according to the invention, the above men-tioned induced voltage
is reduced by slowing the rise and fall of the pulses applied
to the lnput terminals 77a, 77b and 77c by the integrating
circuits 78a, 78b and 78c. It is noted that the fact that the
20 output transistors 58a, 58b and 58c do not opera-te in the
saturation state is one of the reasons why the induced voltage
can be lowered by suppressing the abrupt change of the pulses
at the input.
The emitter resistors 65a, 65b and 65c are connected
to the emitter of the output transistors 58a, 58b and 58c for
the following reason. When the caps-tan motor is rotated by
the pulse signal from the pulse generator 42, because the main
windings 45a, 45b and 45c are excited by the 1-2 phase excita-
tion method, as described hereinbefore, there exists a ~ime
30 when current flows to both main windings (45a and 45b, 45b and
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45a, and 45c and ~5a) at the same -time. On the other }-lalld,
the current Elowing to the main windings 45a, ~5b and 45c is
according to the pulse voltage applied -to the output transis-tors
58a, 58b and 58c and the emitter resistors 65a, 65b and 65c.
And, similarly to the case of operating the capstan motor 25
as a conventional brushless DC motor, a three-phase differential
_circuit is formed by connecting the emitter of the output
transistors 58a, 58b and 58c with a common resis-tor instead of
the emitter resistors 65a, 65b and 65c. Therefore, when the
currents flow at the same time -to the above described two
main windings and when the amplitudes of the pulses applied
to the input terminals 77a, 77b and 77c are slightly different
from each other, the currents flowing to the -two main windings
become very different from each other. In the e~treme casc,
the current flows only to one main winding, and so the step
rotation angle of the capstan motor 25 changes abo~t one step.
For the above reason, the emitter resistors 65a, 65b and 65c
are provided for each of the output transistors 58a, 58b and
58c. The values of the feedback resistors 66a, 66b and 66c
are made large enough compared with those of the emitter
resistors 65a, 65b and 65c.
There will now be described the case of a standard
I-type device as referred to at the beginning of this specifi-
cation, where the standard tape moving speed is 19.05 cm/sec.
In this case, the speed of ro-tation of the capstan motor is
1200 rpm, and the number of gear teeth on the gear 70 is 192.
On the other hand, the frequency of the signal from the wave-
shaplng circuit 9 is set to be 30 Hz, -the same as the frame
frequency of the video signal. At the rotation speed of 1200
rpm (20~ rotations each second) of the capstan motor 25, the
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frequency of -the signal provided from the magnetic head 71
shown in Fig. 2 becomes 38~0 Hz (192x20). As explained with
reference to Fig. 1, this signal is applied -to the 1/2 divider
28 and the 1 divider 29 and there is selected from the selection
circuit 30 a signal with a frequency of 240 Hz, and Eur-ther
the frequency is divided to 120 Hz through the bi-stable
_multivibrator 31. ~he second output having frequency of 120 Hz
from the bi-stable mul-tivibra-tor 31 is changed to a frequency
of 60 Hz by the 1/2 divider 35. This frequency is two times thc
frequency (30 Hz) of the wave-shaping circuit described above.
When the tape moving speed is about 2.4 cm/sec, i.e. 1/8 of
the standard tape moving speed, the signal of the 1/2 divider
28 is selected by the selection circuit 30. When the tape
moving speed is abou-t 1.2 cm/sec, i.e. 1/16 of the standard
tape moving speed, the signal from the amplifier 27 is selected
by the selection circuit 30. Accordingly, the frequency of the
signal from the selection circuit 30 becomes constant
regardless of the moving speed of the magnetic tape 7. The
speed of rotation of the capstan motor 25 for the tape moving
20 speed of 2.4 cm/sec and 1.2 cm/sec is 150 rpm and 75 rpm,
respectively.
On the other hand, when the capstan motor 25 is
rotated by the pulse from the pulse generator 42 is as Eollows,
as described hereinbefore, the capstan motor 25 rotates one
rotation when the number of the pulses applied to the pulse
generator 42 is 48. Therefore, in the case when the tape
moving speed is about 0.6 cm/sec, i.e. 1/32 of the standard
tape moving speed, the signal having frequency of 30 Hz from
the wave shaping circuit 9 is selected by the selection circuit
41. Then, the rota-tion speed of the capstan motor 25 becomes
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37.5 rpm (30 Hzx60 sec/ 48 pulses= 37.5 rpm). When the moving
speed of the magnetic tape 7 is 1/64 of the s-tandard -tape
moving speed, the selection circuit is connected to the 2-
divider ~0. Therefore, there is no pulse applied to the pulse
generator during a period when one magnetic -track is formed
by the rotary head assembly 6 (about a period of one field),
_and the tape is held stationary. Because the signal provided
from the wave-shaping circuit 9 is used as the pulse -to be
applied to the pulse generator 42, when forming the magnetic
tracks successively the number of the pulses applied to -the
pulse generator 42 during a period for forming each magnetic
track is the same. The frequency dividing ratio of the first
gate signal divider 19 is set to be 1/8, and that of the
second to fourth gate signal dividers 20, 21 and 22 is set -to
be 1/2, respectively.
Although the present invention is described herein-
before as being for recording a video signal to the magnetic
tape, in the case of reproducing the recorded video signal
there is also provided the same tape moving speed as that of
recording by using e.g. an oscillator providing a signal
having a frequency of 30 Hz instead of the output signal from
the wave-shaping circuit 9. Of course, the method of repro-
ducing the video signal recorded on the magnetic tape 7 is
the same as that of a conventional magnetic recording and
reproducing device.
As described hereinbefore, according to the present
invention, for the motor for moving the magnetic tape, there is
provided a first rotating state where the current flowing -to
the main windings which generate the driving torque is switched
by the signal indicating the rotational position of the rotor,
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and a second rotating state where -the current flowing -to the
main windings is switched by an additional pulse. For the
range of tape moving speeds from the standard tape moving speed
to the speed at which the playback of the audio signal can be
processed practically, in -the first state the ro-tation phase
of the motor is used, and for a tape moving speed lower than
_the above range the second rotating state is used. Because
the same reference signal is used for both states, the mo-tor
is rotated synchronously with the reference signal, and so
the tape moving speed can be advantageously changed accurately
over a wide range. Fur-ther, there are the advantages -that
wow and flutter characteristics of the audlo signal can be
improved by maintaining the linearity of the magnetic track,
that the interval between the adjacent magnetic tracks can be
kept equal, and that the amount of power consumed for driving
the magnetic tape is small.
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