JPS6141041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching system for a head signal circuit in a helical scan type video tape recorder for professional use.

Conventionally, such commercial video tape recorders (hereinafter referred to as VTRs) use a 2-inch wide magnetic tape called the ampex type, which records a large number of discontinuous recording tracks in a direction almost perpendicular to the direction in which the tape travels. However, in recent years, a helical recording system has been used, which uses a rotating head drum to form recording tracks diagonally in the direction of travel on a relatively narrow magnetic tape of about 1 inch. Scan-type VCRs have come into use. Of these, the most mainstream is a system called SMPTE Type C.

In this SMPTE type C system, the arrangement of each head within the rotating drum is as shown in FIG. In the figure, 1 is a magnetic tape, 2 is a rotating drum, and the magnetic tape 1 is fed in the direction of arrow B relative to the drum 2 rotating in the direction of arrow A. And the head is 3
A set of erase heads (for flying erase), a recording/reproducing head (hereinafter simply referred to as recording head), and a reproduction-only head (for monitoring).
There are three sets of heads, each spaced 120 degrees apart. Each head is composed of two heads, one for video signals (indicated by V) and one for synchronization signals (indicated by S), but for the sake of simplicity, in the following explanation, we will focus on the head for video signals. I will only explain about.

Incidentally, for switching head signals in such a VTR, a circuit as shown in FIG. 2 has conventionally been used.

In FIG. 2, 2 is a rotating drum, 3 is a recording head, 4 is a reproduction-only head, and 5 is an erasing head 6-
8 is a rotary transformer, 9 is a recording signal input, 1
0 is reproduction signal output, 11 is erasure signal input, 12,
13 is a head amplifier, and 14 _-1 and 14 _-2 are switch elements.

The switch elements 14 _-1 and 14 _-2 are switched by control signals so that they are switched to the REC side during recording and to the PB side during playback.

During recording, a recording signal from the input 9 is supplied to the recording head 3 in the rotary drum 2 via the switch element _14-1 and the rotary transformer 6, and recording on the magnetic tape is performed. At this time, the recorded signal is immediately read out by the read-only head 4,
The signal is amplified by the head amplifier 12, taken out from the rotating drum 2 by the rotary transformer 7, and supplied as a reproduction signal to the output 10 via the switch element _14-2 , thereby making it possible to monitor the signal.

At the same time, an erase signal from the input 11 is supplied to the erase head 5 in the rotary drum 2 via the rotary transformer 8, and a flying erase is performed.

Next, during reproduction, the signal read from the magnetic tape by the recording head 3 is taken out from the rotary drum 2 via the rotary transformer 6, and is sent to the switch element 14.
_-1 is supplied to the head amplifier 13, amplified, and then supplied to the output 10 as a reproduction signal via the switch element _14-2 .

As described above, according to the head signal switching circuit shown in FIG. 2, it is possible to easily switch between the recording operation and the reproducing operation that can be monitored simply by operating the switch elements 14 _-1 and 14 _-2 . It has been widely adopted in the past.

However, in the conventional circuit described above, (1) During playback, the signal read out by the recording head 3 is taken out from the rotary drum 2 via the rotary transformer 6 at the same low level, and is further passed through the switch element _14-1. Since the signal is supplied to the input of the head amplifier 13, it is susceptible to attenuation and noise induction, making it difficult to maintain a good S/N ratio.

(2) Two high-performance head amplifiers are required for amplifying the reproduced signal, which increases costs.

There was a drawback.

The object of the present invention is to eliminate the drawbacks of the prior art described above, provide a helical scan type that has a good S/N ratio of reproduced signals, and requires only one head amplifier.
To provide a VTR head signal switching system.

To achieve this objective, the present invention is characterized in that a switch element is housed within the rotating drum and is controlled by an erase signal.

Embodiments of the head signal switching system according to the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which the same or equivalent parts as in the conventional example shown in FIG. 2 are given the same reference numerals.
A detailed explanation thereof will be omitted.

In FIG. 3, 15 _-1 and 15 _-2 are switch elements, 16 is a head amplifier, 17 is an erase signal detection circuit, and 18 is a switch element drive circuit.

The erase signal detection circuit 17 detects the erase signal and sends it to the switch elements 15 _-1 , 15 _-2 via the drive circuit 18.
This circuit operates to switch the switch elements _15-1 and _15-2 to the REC side only while the erase signal is being supplied to the erase head 5, and to switch them to the PB side during other periods. It consists of a circuit that generates an output by envelope detection of the erasure signal, or a retriggerable monostable multivibrator (retrigger circuit) using the erasure signal as a trigger input.

Next, the operation will be explained.

First, during recording, a recording signal is supplied from the input 9 and an erasing signal is supplied from the input 11.

Therefore, the erase signal sent into the rotary drum 2 via the rotary transformer 8 is supplied to the erase head 5 to perform the erase operation, but at the same time is also supplied to the erase signal detection circuit 17, and is sent to the switch element drive circuit 18. Since the output is given to the switch elements 15 _-1 and 15 -2, the switch elements 15 -1 and 15 _-2 are switched to the REC side.
Therefore, the recording signal transmitted from the input 9 to the rotary drum 2 via the rotary transformer 6 is supplied to the recording head 3 via the switch element _15-1 , so that the recording signal is transmitted to the magnetic tape 1 (FIG. 1). Recording of the video signal will take place.

Also, at this time, the signal immediately read out by the read-only head 4 is sent to the head amplifier 1 via the switch element _15-2 which is switched to the REC side.
6 and amplified to a predetermined level,
Since it is taken out from the rotating drum 2 by the rotary transformer 7 and supplied to the output 10, this output 1
The recording operation can be monitored by reproducing the 0 signal as an image using a suitable device.

Next, during playback, no erase signal is supplied to the input 11. Therefore, since no input is given to the erase signal detection circuit 17, the switch element 1
5 _-1 and 15 _-2 remain closed on the PB side.

Therefore, the video signal read from the magnetic tape 1 by the recording head 3 is transferred to the switch elements 15 _-1 , 15
_-2 to the input of the head amplifier 16,
After being amplified to a predetermined level, the signal is taken out from the rotating drum 2 via the rotary transformer 7 and supplied to the output 10.

Therefore, according to the embodiment of the present invention shown in FIG. 3, recording and reproducing operations can be switched in the same way as in the conventional example shown in FIG.

According to this embodiment, since the erase signal is used as a signal for controlling the switch elements 15 _-1 and 15 _-2 provided in the rotary drum 2, the There is no need to provide a signal transmission path. Moreover, at this time, as is clear from FIG. 1, the erasing head is provided at a position with respect to the rotating drum 2 that is 120 degrees further in the rotational direction than the recording head. Between the erasing operation by the erasing head and the recording operation by the recording head, there is a delay of about 5.5 ms, which is the time required for the rotary drum 2 to rotate 120 degrees, so the switch elements 15 _-1 , 15 _- Even if the time required for ₂ to switch from the PB side to the REC side is a little slow, it is not a big problem.

Furthermore, during playback, the signals read out from the magnetic tape by the recording head 3 are amplified to a sufficient level by the head amplifier 16 provided in the rotating drum 2 before being taken out, so the signal is low level. Since the path of the reproduced signal in this state is shortened and is hardly affected by attenuation by the rotary transformer 7, the S/N ratio of the reproduced signal taken out to the output 10 can be maintained sufficiently good.

Furthermore, the amplification of the playback signal for monitoring during recording and the amplification of the playback signal during playback are performed using one head amplifier 1.
6, there is no need to use two expensive head amplifiers.

Note that the switch element 1 in the embodiment of the present invention
_5-1 and _15-2 , as long as the delay time required for the switching operation is within about 5.5 ms, and it can be installed in the rotating drum 2 and used while receiving large centrifugal acceleration. It may be something like
For example, any circuit such as an electronic switch circuit or a relay based on a reed switch that takes into account the mounting condition within the rotating drum can be used.

As explained above, according to the present invention, since the switch element is provided in the rotating drum, only one head amplifier is required, and the S/N ratio of the reproduced signal can be easily adjusted.
In addition, since it is not necessary to add an extra signal transmission path to the rotating drum, it is possible to provide a head signal switching system with a simple structure and low cost, which eliminates the drawbacks of the prior art.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of the arrangement of heads in a helical scan VTR, Fig. 2 is a circuit diagram showing a conventional example of a head signal switching circuit, and Fig. 3 is an example of an embodiment of the head signal switching system according to the present invention. FIG. 1... Magnetic tape, 2... Rotating drum, 3...
Recording/playback head, 4... Playback-only head, 5...
... Erasing head, 6 to 8 ... Rotary transformer, 9
...Record signal input, 10...Reproduction signal output, 11
... Erasing signal input, 15 _-1 , 15 _-2 ... Switch element, 16 ... Head amplifier, 17 ... Erasing signal detection circuit, 18 ... Switch element drive circuit.

Claims (1)

[Claims] 1. In a helical scan video tape recorder that has an erasing head, a recording/playback head, and a playback-only head on a rotating drum, and is capable of monitoring playback signals during recording, a method for switching the signal path for the recording/playback head and playback-only head. A switch element, an erase signal detection circuit that operates the switch element by an erase signal sent to the erase head, and a head amplifier for amplifying the reproduced signal are provided in the rotary drum, and are used to amplify the monitor signal during recording and reproduce during playback. A head signal switching system for a helical scan video tape recorder, characterized in that signal amplification is performed by the same head amplifier by switching heads within a rotating drum.