JPS6171780A - Tape driving circuit - Google Patents

Abstract

PURPOSE:To give correction to a time point when a magnetic tape is stopped by using a reference switch signal which switches the reproduction signal of a rotary magnetic head for each feed period and detecting a phase shift of a control pulse against said switch signal. CONSTITUTION:A signal SV is supplied to a microcomputer 30 as a signal which shows the rotary phases of heads 2A and 2B. While pulses FG and CTL are supplied to the computer 30 as the signals which show the driving speed and direction of a tape 1. At the same time, the pulse CTL is supplied to a monostable multivibrator 27. Then a delay pulse DL of the prescribed width is produced synchronously with the pulse CTL. The pulse DL is also supplied to the computer 30. A control signal CP for tape drive is delivered from the computer 30 and supplied to a servo circuit 24. Thus it is possible to obtain a still reproduction screen free from noises and to perform the feed of frames or the slow reproduction even in case the pulse CTL has a phase shift due to an error of the attachment position of a head 26.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a tape drive circuit for a VTR.

BACKGROUND TECHNOLOGY In a home helical scan type VTR, during playback, if the tape is stopped running while the head is rotated, still playback can be performed. In that case, if the tape is stopped so that the center position of the track on the tape matches the center position of the scanning locus of the head, a clean still playback screen free of noise can be obtained.

(For example, m magazine "Radio Science J, January 1982 issue, published by Japan Broadcasting Publishing Association") There are three methods for stopping the tape in such a positional relationship. The first method is to stop the tape at a predetermined position based on a control pulse recorded on the tape, and the second method is based on a signal that switches the output of two rotating heads every one field period. The third method is to stop the tape at a predetermined position by determining the positional relationship between the head and the tape from the level change of the reproduced FM signal.

Problems to be Solved by the Invention Since there are errors in the mounting position of the magnetic head for reproducing control pulses, the first method does not solve the problem, for example, when the VTR used for recording and the VTR used for reproduction are different. , the tape cannot be stopped accurately at the desired position, resulting in noise on the still playback screen. Furthermore, during frame advance or slow playback, the capstan servo is disturbed, so the second method also produces noise on the screen. Furthermore, in the third method, it takes time until the tape completely stops, that is, until the still screen appears, and furthermore, until the still screen appears,
Noise appears on the screen. Furthermore, either method requires many circuits to determine the timing to stop the tape.

Means for Solving the Problem When playing back with the magnetic tape stopped running, the switching signal that switches the playback signal of the rotating magnetic head every one field period is used as a reference, and the phase shift of the control pulse with respect to this switching signal is determined. The apparatus is provided with means for detecting the detection output and correcting the point at which the magnetic tape is stopped based on the detected output.

When the running of the working magnetic tape is stopped and reproduction is performed, a switching signal that switches the reproduction signal of the rotating magnetic head every one field period is used as a reference, and the phase shift of the control pulse with respect to this switching signal is detected. The detection output corrects the point in time when the magnetic tape is stopped.

Embodiment In FIG. 1, (1) indicates a magnetic tape, on which a color video signal Sc is recorded, for example, in Beta format. That is, the signal So is
One field is recorded adjacent to each other as one diagonal magnetic track, and the azimuth angles of every other track and the remaining every other track are different from each other.

In addition, (2A) and (2B) indicate rotating magnetic heads, and these heads (2A) and (2B) are mutually connected.
The heads (
A head (2a) is provided at a predetermined position close to 2B).

In this case, the heads (2A) and (2a) have the same azimuth angle, and the head (2A).

(2B) is an azimuth angle corresponding to every other track of tape (1) and every other remaining track.

The heads (2A) to (2a) are connected to the rotating shaft (11).
), the head (2A) is rotated at a frame frequency by a motor (12), and the rotating shaft (11) is provided with pulse generating means (13) and (14), for example.
Pulses are taken out alternately every % rotation of ~(2a),
These pulses are supplied to the cent input and reset input of the RS flip-flop (15) and the heads (2A) to (
A rectangular wave signal SV that is inverted every time in 2a) is formed,
This signal Sv is supplied to the drum servo circuit (I6) and compared in phase with the frame frequency reference signal, and the comparison output is supplied to the motor (12) and heads (2A) to (2)
The frequency and phase of rotation in a) are servo-controlled to be constant.

Then, the tape (1) is passed obliquely around the rotating circumferential surface of the heads (2A) to (2a) over an angular range of just over 180 degrees.

Further, (21) is a capstan, and (22) is a capstan motor, to which a frequency generator (23) is rotatably coupled to extract a pulse FG of a frequency corresponding to the running speed of the tape (1). This pulse FG is supplied to the capstan servo circuit (24) to form a predetermined drive voltage, and this drive voltage is applied to the motor (22).
During normal playback, the tape (1) is run at a predetermined speed. Note that (25) is a pinch roller.

Further, a magnetic head (26) is provided in contact with the tape (1), and during normal reproduction, this head (26) reproduces a frame frequency control pulse CTL from the tape (1), and this pulse CTL is transmitted to the servo circuit. (24) and is supplied to the head during normal playback (
The tracking of 2A) and (2B) is servo controlled.

Therefore, reproduction signals of the tape (11) are obtained alternately from the heads (2A) and (2B) every one field period, but the reproduction signal of the head (2A) is obtained from the switch circuit (4).
), and the reproduction signal of the head (2B) is
During normal playback, the signal is supplied to the switch circuit (4) through the switch circuit (3) connected as shown in the figure.

Then, the signal Sv is supplied to the switch circuit (4) as a control signal, and the switch circuit (4) sends the signal to the head (2A).
, (2B) are successively extracted, this reproduced signal is supplied to a processing circuit (5) to be converted into an original color video signal, and this signal is extracted to a terminal (6).

In addition, (30) indicates a microcomputer for system control, (31) its CPU, (32) a ROM in which the program is written, (33) a RAM for a work area, and (33) an input board. , (34)
is an output port. Various programs for operating the VTR, including the routine (60) shown in the flowchart shown in FIG. 2, are written in the ROM (32).

Then, the signal SV is supplied to the microcomputer (30) as a signal indicating the rotational phase of the heads (2A) and (2B), and the pulses FG and CTL are supplied to the microcomputer as signals indicating the running speed and running position of the tape (1). (3o). Further, pulse C: TL 75 is supplied to the monostable multivibrator (27) to form a delayed pulse DL that is synchronized with the pulse CTL and has a predetermined pulse width, and this pulse DL is supplied to the microcomputer (30). A tape running control signal CP is output from the microcomputer (30), and this signal CP is supplied to the servo circuit (24).

Note that the pulse OL originally uses tape (
This is a timing signal when applying a brake to the running of the tape (1). When there is no phase shift in the pulse CTL, the brake is applied to the running of the tape (1) from the falling edge of the pulse D, and the tape (1) is correct. It stops at the still playback position.

Further, (41), (42), . . . are various operation switches including a Bose switch and a frame advance switch, the outputs of which are supplied to the microcomputer (30).

Furthermore, FIG. 3 is a waveform diagram of each signal at time t.

The period after time ts is normal reproduction. That is,
During this normal playback, as shown in Figure A, the signal S
V is inverted every field period in synchronization with the rotation of the heads (2A) and (2B).

Furthermore, since the tape (11) is running at a predetermined constant speed, the pulse CTL is obtained every frame period as shown in B of the same figure, and the pulse F as shown in C of the same figure.
G is obtained at a constant high frequency. In this case, as mentioned above, there is an error in the mounting position of the head (26), so if the VTR used for recording and the VTR used for playback are different, there will also be an error in the phase of the pulse C. , signal S
If V is used as a reference, the phase of the pulse CTL is shifted within an allowable error.

Further, pulse OL is a delayed pulse of pulse CTL,
As shown in the figure, it rises when the pulse CTL rises and falls after a predetermined period T.

As shown in the same figure, when the pause switch (41) is turned on at any point in time during normal playback, the routine (60) is executed by the microcomputer (3) and the still playback mode is set. Ru.

That is, when the switch (41) is turned on at time to, the routine (60) starts from step (61), and the process proceeds to step (62).
), the falling edge of pulse CTL is checked,
This step (62) continues until the pulse CTL falls.
is repeated. Then, when the pulse CTL falls at time t1, the process starts from step (62) to step (6).
3), in this step (63), the software counter CNTR starts to measure time from time t1, and then the process goes to step (64).
), the rise of the signal Sv is checked, and this step (64) is repeated until the signal Sv rises.

Then, when the signal Sv rises at time t2, the process proceeds from step (64) to step (65), and in this step (65) the counter CNTR is stopped from counting. Therefore, this counter CNTR measures the period τ between time points t1 and t2, and this period τ indicates the phase shift of the pulse CTL with respect to the signal Sv.

The process then proceeds from step (65) to step (71), in which the falling edge of the pulse DL is checked, and step (71) is repeated until the pulse DL falls. Then, when the pulse DL falls at time t3, the process proceeds from step (71) to step (72), and in step (72), a wait (time wait) corresponding to the period τ is performed, and from time t3, the process proceeds to step (72). At time t4 after τ, the process proceeds to step (73), in which the signal CP causes the motor (22) to move through the servo circuit (24).
The brakes are applied at , and therefore from time t4 the tape (
11 is applied, and the running of the tape (1) completely stops at time t5 after a predetermined period from time t4. In this state, as will be described later, the tape (1) has stopped at the correct stay playback position. Also, time t4
After that, pulse CTL and DL can no longer be obtained, and
After time t5, pulse FG is no longer obtained.

Further, in step (73), the signal HD rises from time t4 as shown in the waveform diagram F, and this signal HD switches the switch circuit (3) to the opposite state as shown in the diagram, so that the reproduction signal of the head (2a) is changed. Through the switch circuit (3), and further through the switch circuit (4), the processing circuit (5)
supplied to Further, a pseudo vertical synchronizing pulse QSVD is formed in step (73), and this pulse QSVD is supplied to the processing circuit (5). Therefore, a color video signal of still reproduction is obtained at the terminal (6) from time t4.

Further, the process proceeds from step (73) to step (74).
In this step (74), the period (t4~
ts ) weights are performed.

Then, at time t6, the process proceeds to step (81), and in this step (81), the pause switch (
41) is checked and the next step (82)
If the frame forwarding switch (42) is checked in the step (81), and the switch (41) is on and the switch (42) is off, that is, when still playback is specified.

(82) is repeated.

Then, when the pause switch (41) is turned off at an arbitrary time t6, the process starts from step (81) to step (8).
3), and in this step (83), the VTR is put into normal playback mode. That is, this is the opposite process to the process in step (73), and the signal C
P causes the motor (22) to pass through the servo circuit (24).
) is driven to drive the tape (1) to run at a constant speed, and as the signal HD falls, the switch circuit (3) is connected to the state shown in the figure and the head (2A) is driven.
, (2B) are supplied to the processing circuit (5). Additionally, the pseudo vertical synchronization pulse QSVD is also no longer formed. Therefore, normal reproduction is performed after time t6.

Subsequently, the process of the microcomputer (30) proceeds to step (84), and in this step (84), another counter C0NT is started by software to begin measuring time from time t6, and then the process proceeds to step (84). 85),
In step (85), the pause switch (41) is checked, and when it is off, the process moves to step (86), and in step (86), the counter C0NT determines whether a predetermined period Tc has elapsed since time tG. If the period T6 has not elapsed, the process returns to step (85), and if it has elapsed, the routine (60) is ended in step (87).

In this case, the period T6 is a period until the pause is released at time t6 and the servo circuit (24) stabilizes, that is, a period until the tape (1) reaches a steady speed.

Further, in step (85), the pause switch (41
) is on, the process returns to step (71) and the operations from point L2 onwards are repeated.

Therefore, through these steps (85) and (86), the pause is released at time t6, and then the pause switch (
41) is turned on, it starts from time t6 on the tape (
If it is within the period TG until the running becomes stable in 1), the period τ measured in the previous period (h to k) will be used from time t3. That is, the servo circuit (24)
If the pause switch (41) is turned on again before the period τ has stabilized, even if the period τ is measured in steps (61) to (65), it will be inaccurate, so the measurement will not be performed and the previous value τ will be Once used, tape (1) stops.

On the other hand, when steps (81) and (82) are repeated, if the frame feed switch (42) is turned on,
The process proceeds from step (82) to step (91),
In this step (91), the fall of the signal Sv is checked, and step (91) is repeated until it falls.

Then, when the signal Sv falls, the process starts at step (9).
1) to step (92), and this step (92
), the same process as step (83) is performed, that is, the motor (22) is driven by the signal CP through the servo circuit (24) to run the tape (1) by a predetermined distance, and the signal HD is turned on. By lowering, the switch circuit (3) is connected to the state shown in the figure, and the head (2) is connected to the state shown in the figure.
The reproduced signals of A) and (2B) are supplied to the processing circuit (5). The pseudo vertical synchronization pulse QSVD is no longer supplied.

Then, the process continues from step (92) to step (7).
Returning to step 1), therefore, in step (71) the signal S
If the falling edge of v is detected, the tape (1) is stopped again in step (75) and still playback is started, after which steps (81) and (82) are repeated.

In other words, each time the frame advance switch (42) is turned on, the tape (1) is alternately advanced and still reproduced to advance the frame.

In this way, frame forwarding is performed by repeating stay playback or stay playback, but in this case, the head (2
This signal S is based on the signal SV for switching the reproduced signals of A) and (2B) every one field period.
Since the phase shift of the control pulse CTL with respect to v is detected and the timing at which the tape (1) is stopped is corrected based on this, the tape (1) can be stopped at the correct position and still playback can be performed.

That is, if the rising point of the signal SV is used as a reference, from the waveform diagram, t2-τ-Δτ+T+1 frame period+τ=1+Δ
τ: Since it is the pulse width of pulse CTL, t4 = t2 - Δτ + T + 1 frame period,
The time point t4 is not related to the phase shift period τ of the pulse CTL with respect to the signal Sv, and at this time, the period Δτ, T is constant. Therefore, time t4 is at a constant time position with respect to time t2. Then, since a brake is applied to the running of the tape (fl) with reference to time t4, by sesotiging this brake amount in advance, when the tape (1) stops at time t5, the head (2A)
, (2a) can scan the center position of the track, and therefore can obtain a noise-free still playback screen.

Thus, according to the present invention, even if there is a phase shift in the control pulse CTL due to a positional error in mounting the head (26), noise-free still playback screen, frame advance, or slow playback can be performed. Furthermore, a tracking circuit for still playback can be omitted, and discrete circuits are also almost unnecessary.

Effects of the Invention When the running of the magnetic tape is stopped and reproduction is performed, a switching signal for switching the reproduction signal of the rotating magnetic head every one field period is used as a reference, and a phase shift of the control pulse with respect to this switching signal is detected. Since the point at which the magnetic tape is stopped is corrected based on this detection output, the head (26) can be installed to maintain a noise-free still playback screen and frame feed even if there is a phase shift in the control pulse CTL due to positional errors. Alternatively, slow playback can be performed. Furthermore, a tracking circuit for still playback can be omitted, and discrete circuits are also almost unnecessary.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an example of the present invention, and FIGS. 2 and 3 are diagrams for explaining the same. (5) is a processing circuit, (16) and (24) are servo circuits, and (30) is a microcomputer.

Claims (1)

[Claims] In a helical scan type VTR, when the magnetic tape is stopped and played back, the switching signal that switches the reproduction signal of the rotating magnetic head every one field period is used as a reference, and the phase shift of the control pulse with respect to this switching signal is calculated. A tape drive circuit that detects the magnetic tape and corrects the point at which the magnetic tape is stopped based on the detection output.