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Description  |
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FIELD OF INVENTION
This invention relates to a video cassette tape recorder for recording
and/or reproducing video signals in a recording medium, and in particular
to a tape transport control for automatically placing a tape in position
for recording or reproduction after insertion of a tape cassette into the
recording device.
BACKGROUND OF THE INVENTION
Video tape cassette recorders (VCR's) are widely used to record and/or
reproduce video signals on a recording medium (tape).
In certain fields of application, as for example in the medical field, it
is desirable not only to simplify the operation of the recorder, but also
to reduce the time interval between the instant at which the RECORD mode
is activated and actual recording commences. Similar considerations apply
to the interval between actuation of the PLAY mode and commencement of
play-back.
An example of this occurs in x-ray fluoroscopy employing an adjacent video
cassette recorder where activation of the RECORD mode begins at the same
time the x-ray apparatus is activated. By minimizing the time of
activation of the VCR, the patient can be exposed to substantially less
harmful radiation.
In currently available video cassette recorders, the tape cassette is
inserted into a cassette holder which is retracted into the machine.
Mechanical fingers then withdraw the tape into a position where reel
brakes are applied.
In the conventional VCR, this position is referred to as the "STOP" mode.
In the "STOP" mode, the machine is in its stand-by state, i.e., nothing
further happens until a function button is depressed. The function buttons
are: STOP, FORWARD, REVERSE, PAUSE, PLAY, RECORD, AND EJECT. The
mechanical functions of these states in a conventional VCR are as follows:
1. The STOP mode has been described above.
2. FORWARD:
A. Reel brakes are released.
B. Torque on the reels is adjusted so that the tape is accelerated in a
forward direction at a high rate of speed.
3. REVERSE:
A. Reel brakes are released.
B. Torque on the reels is adjusted so that the tape is accelerated in the
reverse direction at a high rate of speed.
4. PLAY:
A. Take-up reel brakes are released and torque on the take-up reel is
adjusted for proper tape tension.
B. Mechanical fingers withdraw additional tape from the tape cassette and
transfer it to the thread ring.
C. The thread ring pulls the tape around the play/record heads and then to
the capstan shaft.
D. A solenoid is activated to engage the pinch roller which pinches the
tape between a rubber roller and the rotating capstan shaft. At the same
time, the supply reel brakes are released and tension is adjusted for
approximately 75 g.
E. The capstan shaft accelerates the tape up to a tape speed of 9.53 cm/sec
and maintains this speed during the play-back mode. The average time
required to begin playing back pre-recorded information on the tape is
approximately between 3-5 seconds.
5. PAUSE:
A. The machine must be in the play mode before the pause mode can be
activated.
B. The pinch roller is released from the capstan shaft causing the tape to
stop moving.
6. RECORD:
The sequence of steps in the RECORD mode is identical to those listed for
the PLAY mode. It still requires 3-5 seconds before the machine is
actually recording information which is too long an interval for many
applications and can result in a loss of information.
7. STOP:
A. The pinch roller is disengaged from capstan shaft, stopping tape
movement.
B. Torque on the reels is adjusted so that the take-up reel rewinds tape
onto it and the supply reel is locked.
C. The thread ring is activated to guide tape off the record/play heads,
then transfers it to mechanical fingers which retract into the stop
position.
8. EJECT:
A. Mechanical fingers insert tape into tape cassette.
B. The tape cassette in elevated from the machine.
C. The tape cassette is ejected from the tape cassette holder.
SUMMARY OF INVENTION
In the video cassette recorder (VCR) according to the invention, the time
to go from STOP mode to the PLAY-BACK or RECORD mode is materially
reduced. This is accomplished as follows:
1. The tape cassette is inserted into the machine.
2. The cassette holder is retracted into the machine.
3. The take-up (TU) reel brake is released and torque on the reel is
adjusted for suitable tape tension.
4. Mechanical fingers withdraw tape into the machine and then transfer it
to the thread ring.
5. The thread ring pulls tape around over the play/record heads and then to
the stationary capstan shaft.
6. A solenoid is activated to engage the pinch roller which pinches the
tape between a rubber roller and the stationary capstan shaft.
7. Tension on the tape is then adjusted to approximately 3-4 grams on the
supply reel side and 60-100 grams on the take-up reel side.
The tape is now parked in a mode that except as hereinafter noted will be
referred to as the "STOP" mode. The length of time to place the tape in
this position is 3-5 seconds. The machine is now ready for recording or
playback. It will be appreciated that the term "STOP" mode, as it refers
to the present apparatus references to a configuration which differs from
the configuration of a conventional machine when in a "STOP" mode. Such
conventional configuration has been heretofore described.
In order to play-back and/or record, the following sequence takes place:
A. The reel torque on the supply side is increased up to 75 grams.
B. The capstan shaft is activated which accelerates the tape to 9.53
cm/sec.
The length of time to bring the tape from the STOP mode to the play-back
and/or recording mode is now only approximately 250 milliseconds.
To stop the tape, i.e., bring the machine to a STOP position, the capstan
shaft is electronically braked to zero rotation and the supply reel torque
adjusted to reduce the tape tension to 3-4 grams. The length of time for
the machine to enter this mode is approximately 100 milliseconds.
The machine also has several other functions which are:
PAUSE:
Can only be entered if the machine is initially in the play mode. When the
pause button is depressed, the capstan shaft is electronically braked to
zero. Tensions remain as they were in the PLAY mode.
FORWARD and REVERSE SLOW MOTION:
These modes can only be entered from the PAUSE mode. While in the PAUSE
mode, if the FORWARD or REVERSE buttons are depressed, and held in the
capstan shaft will begin to rotate at the rate of approximately 1 video
field per 2 seconds in the forward (or reverse) direction, then will
accelerate to approximately 1/5 normal speed. This gradual acceleration
from stop to 1/5 normal speed takes approximately 5 seconds.
FORWARD/REVERSE:
A. The pinch roller is disengaged from the capstan shaft.
B. The supply reel is locked.
C. The thread ring is activated to guide the tape off the record/play
heads, then transfers it to mechanical fingers which retract it away from
the record/play heads.
D. The supply reel brake is released.
E. Torque on the reels is adjusted so that the tape is accelerated in the
forward (or reverse) direction at a high rate of speed.
F. When the STOP button is depressed or the end of the tape is reached, the
following sequence takes place:
1. Torque on the reels is adjusted so that the tape is smoothly brought to
a halt.
2. The supply reel is locked.
3. Mechanical fingers transfer tape to the thread ring which guides the
tape around the play/record heads and then to the stationary capstan
shaft.
4. A solenoid is activated to engage the pinch roller which pinches the
tape between a rubber roller and the stationary capstan shaft. The machine
is now in the STOP mode once again.
EJECT:
From the REVERSE or FORWARD mode the EJECT mode is identical to that of the
conventional machine.
Likewise, from either the PLAY or RECORD modes the EJECT mode follows the
sequence for FORWARD or REVERSE and then that of the known machine.
The logic for effecting these sequences are partially incorporated in a
micro-processor.
OBJECTS OF THE INVENTION
An object of the present invention is accordingly to provide a tape
transport control for a video cassette recording and reproducing device,
enabling the recording medium to be in readiness for play-back or
recording without significant loss of time.
A further object of the invention is to provide a video cassette recorder
for applications wherein recording of images is facilitated without loss
of significant information due to load and unload times.
These and further objects of the invention will appear as the specification
progresses. The invention will be described in connection with a preferred
embodiment from which the foregoing objects and other advantages will
appear. However, the invention is not limited to this particular
embodiment, but is defined in the following claims.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described with reference to the accompanying drawing
in which:
FIG. 1, shown as FIGS. 1--1 and 1-2 is a schematic drawing of a circuit
used to control the operation of the video cassette recorder according to
the invention.
FIG. 1a is a schematic drawing of the change-over network in FIG. 1.
FIG. 2 is a plan view, in perspective, showing the tape transport mechanism
for the video cassette recorder embodying the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
A video cassette recorder (VCR) in accordance with the invention, comprises
a tape transport mechanism (FIG. 2) and suitable means for withdrawing the
tape into, and guiding the tape around a cylinder containing the video
record/play heads.
A number of operations must be performed after a cassette holding the tape
is placed in a cassette holder (see FIG. 2). Briefly, when the cassette is
placed in the cassette holder, fingers withdraw the tape which is then
threaded through the machine around a cylinder and positioned for
play-back or recording. The tape is then in the STOP mode.
The machine may then be activated for either play-back or recording. During
play-back, information on the tape is converted to an electrical signal by
the recording/play-back heads while the tape is transported past the
heads. This electrical signal is demodulated and processed to produce a
visual image.
Likewise, during recording, a video signal generated by a camera or like
video signal producing device coupled to the recorder is modulated into an
r-f signal and recorded on the tape as it passes the recording heads.
Since the tape may already have information recorded thereon, during the
recording the tape passes an erase head which is activated to erase any
signals in the tape before passing the recording heads.
It may be desired, to position the tape to a particular section.
Accordingly, provision is made to advance the tape by moving the tape
rapidly in the forward direction, otherwise referred to as the FORWARD
mode. Likewise, it may be desired to return rapidly to an earlier section
and this is done by moving the tape rapidly in a reverse direction or the
REVERSE mode.
It may be desired to view a particular field during playback, and for this
purpose, a pause control is provided.
It may also be desired to view a particular section of tape in slow
motion--this can be either in a forward or reverse sense. When in this
mode, the FORWARD and REVERSE buttons function as slow motion controls.
Other functions are to stop the tape movement, to rewind the tape, and
finally upon completion of the unthreading process to eject the cassette
from the machine.
Each of these functions will be described with reference to FIG. 1, which
shows in detail the circuit for controlling the tape transport mechanism,
a portion of which is shown in FIG. 2.
Only essential elements and details of the VCR according to the invention
have been shown in the drawing to simplify the understanding of the
machine and its operation. It is to be understood that other features may
be incorporated, and even modifications made therein without departing
from the scope of the invention which is pointed out in the claims.
Referring to FIG. 1 of the drawing, the circuit shown there instructs a
microprocessor, already contained in the machine to perform different
functions than it was originally designed to do. Thus, when the tape is
inserted into the machine, the microprocessor is instructed by this
circuit to go into PLAY mode--as that term was defined for a conventional
machine. However, in the present apparatus, the capstan motor is turned
off and the video input is connected to the video output through a relay;
also the supply tension is reduced (to eliminate play/record head to tape
contact, thus eliminating head wear and tape damage). After the tape is
loaded and the PLAY button depressed, the capstan motor is activated,
tension is set to normal and the video output is connected to the
demodulator circuit.
When any mode except PAUSE or RECORD is selected from the front panel
controls, the circuit momentarily activates the STOP mode, then the
selected function is initiated. When the STOP button is depressed, the
microprocessor is instructed to momentarily enter the (conventional) STOP
mode, then enter the (conventional) PLAY mode--but with the capstan off
and decreased supply tension.
The circuit will be described by referring to the various operations to be
programmed.
A. INSERTING TAPE INTO MACHINE TO ENTER STOP MODE
When tape is inserted into the machine, the end of tape sensor 110 is
triggered and produces a low-to-high transition, which appears at the
input 12 of pulse generator 14. The output 16 of pulse generator 14
produces a positive-going pulse of approximately one-second duration,
which appears at the input 18 of pulse generator 20. Pulse generator 20
produces a positive-going pulse approximately one-half second duration
appearing at the output 22. The pulse generated by pulse generator 20
appears at the input 24 of pulse generator 26 which produces a pulse of
approximately three seconds duration which appears at the output 28 of
pulse generator 26 and causes PLAY buss 30 to go low through interlock 32
(NAND) which has an input terminal 34 directly connected to the output 28
of pulse generator 26 and an output terminal 36 to which the PLAY buss is
connected. Interlock 32 inhibits the PLAY pulse if the machine is in the
EJECT, FAST FORWARD or REWIND modes.
B. PLAY MODE
With the tape inserted into the machine and wrapped around the play/record
heads, the capstan motor will not be running. The PLAY mode activates the
capstan motor in the following manner:
When the PLAY switch 38 is depressed, it creates a high-to-low transition
which passes through inverter 40 and sets latch 42. Output 44 of latch 42
goes low which deactivates tension control 46. It also activates the
capstan motor 48 through interlock 50 (NAND) only if the LOAD END switch
102 is activated. By "load end" is meant the condition whereby the tape is
threaded completely around the cylinder assembly. Outupt 44 of latch 42 is
also coupled to interlock 123 via input 121. If the LOAD END SW is
activated, then interlock 124 output 129 goes low and activates the play
lamp. If the play lamp is lit then interlock 100 is inhibited, thus
shutting off the stop lamp. Output 52 of latch 42 is coupled through
interlock 54 (NAND), (unless the record lamp 56 is lit) to interlock 58
(NAND), via delay network 64, and then to video change-over switch 60,
which switches the video output 62 from LOOP THROUGH to PLAY mode.
Interlock 58 inhibits relay switch 60 command until the machine is in the
LOAD END mode.
A delay circuit 64 between interlock 54 and interlock 58 inhibits
change-over switch 60 from switching for about 500 milliseconds. This
allows time for the recorder servo motors (not shown) to fully synchronize
before switching the relay.
C. RECORD MODE
The RECORD mode can only be entered when the PLAY and RECORD buttons are
depressed together. When the PLAY switch 38 is depressed, a low level is
presented to input terminal 66 of interlock 68 (OR). When the RECORD
switch 70 is depressed, a low is presented at input terminal 72 of
interlock 68 causing output terminal 74 to drop to a low which activates
RECORD buss 76. Diode 75 is required to insure that the microprocessor
(not shown) has two lows simultaneously on the RECORD and PLAY busses. The
microprocessor will then activate the record lamp 56, which inhibits
changeover switch 60 from switching through interlock 54.
D. STOP MODE
When STOP switch 78 is depressed, a high-to-low transition is coupled
through interlock 80 provided that end-of-tape sensor 110 is low. This
transition, inverted by end-of-tape sensor interlock (NOR) 80, triggers
pulse generator 20 through input terminal 18 producing a pulse at output
terminal 22 which is coupled through invertor 84 whose output 86 is
coupled to STOP buss 88. Output terminal 22 of pulse generator 20 is also
coupled to pulse generator 26 which triggers the PLAY buss 30 through
interlock 32. The longer time out of pulse generator 26 insures that after
the STOP buss has received a pulse, the PLAY buss will still be activated
for a short time so that the tape will remain threaded. A pulse from pulse
generator 20 also appears at input terminal 90 of latch 92. Latch 92
enables interlock 32 through interlock 94 via input terminal 96 of
interlock 32 and allows pulses from pulse generator 26 to reach PLAY buss
30. STOP lamp 98 will be lit through interlock 100 only when the LOAD END
mode switch 102 is activated. However, the STOP LAMP will be inhibited
through input terminal 104 of interlock 100 whenever PLAY LAMP 106 is lit.
STOP LAMP 98 will be prevented from lighting by inverter 103 whenever the
LOAD END Mode switch 102 is not activated.
E. FORWARD MODE
When the Fast Foward switch 108 is depressed, a low is coupled through
input terminal 111 of NORMAL CHANGE OVER NETWORK 112 (See FIG. 1A) which
activates FAST FORWARD buss 114 through a low on output terminal 116.
Diode 118 (FIG. 1) connected to output terminal 116 pulls interlocks 120
(OR) and 124 (NAND) via input terminals 122 and 126 low and resets latch
92 through inverter 128. Latch 92 causes an inhibit pulse to appear at
input 96 of interlock 32. This prevents any pulses from activating the
PLAY buss when the FORWARD buss is activated. The output of interlock 120
provides a STOP pulse into the pulse generator 20 by coupling through
interlock 80. This STOP pulse is inhibited by interlock 120 if the machine
is in the PLAY mode. Interlock 124 causes latch 42 to reset, thus shutting
off CAPSTAN MOTOR 48 and causing video change-over switch 60 to switch
from PLAY mode to LOOP THROUGH mode.
F. REWIND MODE
When Rewind Switch 125 is depressed it causes a low at terminal 127 of
change-over network 112. Output terminal 130 is coupled directly to REWIND
buss 132. REWIND buss 132 is also connected through diode 134 to
interlocks 120 and 124, and inverter 128 and performs the same functions
as those components in the FORWARD mode.
G. EJECT MODE
Whenever EJECT switch 136 is depressed, it causes a low to activate STOP
buss 88 via direct connection. If there is no tape in the cassette holder,
as detected by store end switch 144, then when EJECT switch 136 is
depressed, the low signal is coupled into interlock 138 through input
terminal 140 and then on to EJECT buss 142. Interlock 138 (OR) inhibits
this pulse unless the STORE END switch 144 is depressed. Switch 144
activates when the mechanical fingers that withdraw the tape from the
cassette are in their store position.
If there is tape in the machine and DRAW END switch 146 is activated, then
interlock 148 (NOR) to which switch 146 is connected through input
terminal 150 resets latch 152.
This will cause output 154 of the latch to hold EJECT buss 142 low forcing
the machine into the EJECT mode. It will also cause output 156 to latch
high, inhibiting any pulses from reaching PLAY buss 30 through interlock
94 and interlock 32. As the machine unthreads and passes the DRAW END
switch 146, a low-to-high transition is presented at the input terminal
158 of pulse generator 160, the output 162 is coupled to input 164 of
latch 152. This causes latch output 154 and 156 to reverse states, thus
opening interlocks 94 and 32 and releasing EJECT buss 142.
H. PAUSE MODE
The pause mode can only be entered from the PLAY mode because PAUSE switch
166 (Reference FIG. 1A) is inhibited by latch 42 whenever it is in the set
condition. PAUSE switch 166 is connected to interlock 168. Input terminal
170 is connected to latch 42.
If the machine is in the PLAY mode when the PAUSE switch is depressed, a
low appears at input 170 of interlock 168 and at the input terminal 172 of
pulse generator 26. The output of interlock 171 enables search buss 175,
thus braking the capstan motor to a stop. This low at input terminal 172
resets pulse generator 26. This is necessary to prevent PLAY buss 30 and
SEARCH buss 175 from being simultaneously activated if pulse generator 26
has not timed out.
The pause mode causes the capstan motor to brake to a stop, via search buss
175, thus, stopping tape motion, and holding one video field on the
monitor. The pause mode is inhibited unless the machine is in the play
mode initially. When in the PAUSE-mode, if the forward button or the
rewind button is depressed, the capstan motor is accelerated in the
forward or the reverse mode, up to 1/5 normal speed.
FORWARD AND REVERSE SEARCH MODE
When the PAUSE switch 166 is depressed, a high to low voltage transition is
coupled into interlock 168 of the change-over network 122 (See FIG. 1a),
which inhibits its output, if latch 42 is in the set condition. If latch
42, is not in the set condition, then the pause voltage level shift is
sent on to interlock 171, which inhibits any level changes at its output,
if interlock 50, via input 173, is in its inhibit condition (i.e. load end
switch 102 is not activated). If interlocks 168 and 171 allow the voltage
transitions to pull the search buss 175 low, they also will set latches
181 and 191, causing their outputs 183 and 193 to go high.
If FORWARD switch 108 is depressed, a high to low voltage transition is
presented to switches 185 and 187, via input 111. If latches 181 and 191
are set, then switch 185 will inhibit any voltage transitions to the fast
forward buss 114, and switch 187 will allow a voltage transition at the
FORWARD SEARCH buss 176. Conversely, if latches 181 and 191 are in their
reset condition (i.e. 183 and 193 low), then switch 187 will inhibit any
changes to FORWARD SEARCH buss 176, and switch 185 will allow a voltage
transition at the FORWARD buss 114.
If rewind switch 125 is depressed, a high to low voltage transition is
presented to switches 179 and 189. If latches 181 and 191 are in their set
condition, (i.e. 183 and 193 are high) then switch 179 will inhibit any
voltage transitions to the rewind buss 132, and switch 189 will allow a
voltage transition at the REWIND SEARCH buss 175.
A voltage transition at pulse generator 20 (stop command) causes latches
181 and 191 to reset via inverter 84.
The pause timer 182 will time out after approximately one and one-half
minutes after which it sends a pulse to input terminal 18 of pulse
generator 20 causing the machine to go into STOP mode. This prevents
damage to the tape and heads if for any reason there is no tape movement
for one and one-half minutes.
It the SEARCH buss goes low during this one and one-half minute time out,
the pause timer resets via diodes 184, 177, or 181, and activates once
again.
If the machine is in the PAUSE mode then any level changes at input
terminals 111 and 127 of change-over network 112 will be transferred to
output terminals 178 and 168. Therefore, if the FORWARD switch is
depressed, a low will appear at input terminal 111. This will cause output
terminal 178 which is connected to the FORWARD SEARCH, buss 176 to go low.
It will also reset and hold PAUSE timer 182 to zero for the duration of
the low via diodes 131 and 184. Also the low at 178 is coupled through a
diode 211 to ramp generator 71 which starts a ramp signal that controls
the speed of capstan motor (not shown). The longer the low is maintained,
the faster the capstan motor goes, up to a limit of approximately 1/5
normal speed.
Operation of the REVERSE SEARCH mode is similar to that of the FORWARD
SEARCH mode.
J. VIDEO CHANGE-OVER RELAY
In all modes except PLAY, this relay by-passes the video input and output.
During the PLAY mode the relay connects the video output to the
demodulator circuit 186 and connects the input to a 75 ohm resistor (not
shown). This resistor loads the automatic gain control (AGC) circuits in
the modulator.
K. AUTO STOP
When tape counter 37 of the machine (not shown) reaches zero and AUTO mode
switch (not shown) is in the SEARCH position, terminal 79 of interlock 80
goes low initiating the same sequence as the STOP mode by a high-to-low
transition.
MECHANICAL OPERATION
The tape transport mechanism shown in FIG. 2 comprises a rotating cylinder
194 housing the video record/play heads around which the tape 196 after it
leaves the cassette 198 in which the supply reel 200 delivers the tape and
a take-up reel 202 winds the returning tape.
After leaving the supply reel, the tape passes an erase-head 204 which
erases, or removes, information on the tape during the recording mode so
that blank tape is presented to the rotating cylinder 194.
The tape, after passing poles 208, 210, and 212 which guide the tape, winds
around a supply tension pole 214 which senses tension of the tape during
play-back and recording, and thence, around pole 216 to cylinder 194.
After leaving cylinder 194, the tape passes over the audio
recording/play-back head 206 after passing pole 218, and thence, over
capstan shaft 220 which drives the tape when pinch roller 222 engages the
tape.
After passing over pinch roller 222, the tape is guided by return poles 224
and 226 and then over pole 228 and around pole 230, the position of which
is fixed by take-up loading arm 232. The positions of poles 214 and 236
are converted to an electrical value by differential transformers 234 and
215, which converts the pole positions into electrical voltages.
The differential transformer outputs go to a servo circuit (not shown)
which in turn, controls reel motor torque.
The tape continues past take-up tension pole 236 and is guided to take-up
reel 202 by poles 238 and 240.
Having thus described the invention in connection with a specific preferred
embodiment, other modifications will be apparent to those skilled in the
art.
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