DE4414147A1 - Recording digital signals on magnetic tape - Google Patents

Abstract

An improved process for utilising the storage capacity of magnetic tape involves the use of a helical track segmented arrangement with four segments, each with separate heads. The tape is driven in both directions at constant speed and the maximum recording rate is higher than the input data rate. The tape is recorded in the forward direction until the end is reached and the tape direction is reversed with recording in the spaces formed within track segments.

Description

The invention is based on a recording method the preamble of claim 1.

It is known that in digital Video magnetic tape recording systems DVC (Digital Video Cassette) a high data rate (25-50 Mbps) at the same time long play time occurs. MPEG (Motion Picture Expert Group) has a very complex data reduction system Motion estimation, interpolation and bidirectional prediction on. Great effort arises in the encoder, in which this Arithmetic operations are to be created from the source material. Of the Decoder receives the inverse calculation instructions, transmitted and reconstructs the picture from it. This coding method is very effective, but unbalanced (great effort in the encoder and low complexity in the decoder), so its use mainly in the field of transmission systems for digital Images will be made, e.g. B. digital television with Data rates between 2. . 8 Mbps for SDTV and 6. . . 24 Mbps for HDTV. This becomes a complex one for each program to be transferred Encoders needed in the studio, and simple decoders evaluate the incoming data stream from the user.

Since these signals should also be recorded and this very much can be done effectively digitally at the data-reduced level, at the moment only digital magnetic tape recorders comply the DVC system in question, which with sufficient playing time can process the corresponding data rate. The MPEG The data stream becomes transparent, i.e. unchanged recorded and also released during playback, so that the decoder made no difference between transmitted and sees recorded data.

A recorder is expecting continuous recording data stream of z. B. 25 Mbps, but there is only one continuous ierlicher / variable data stream of z. B. 8 Mbps (SDTV) Available. It is necessary to adjust the recording data rate  agile. The surplus available should not lost, but used to extend the season become.

The invention has for its object a Record Ver drive to create with the existing storage capacity a magnetic tape can be better used. This task is by the features of claim 1 specified in the invention solved. Advantageous developments of the invention are in the Subclaims specified.

The recording method according to the invention for DVC devices with a season extension is marked by a constant belt feed speed with partially segmented Helical track recording as well as a Bi-directional recording operation when recording and re-recording gift.

In the method according to the invention can only by writing a section of the helical track (e.g. 1/4), a so-called Segment of this can be achieved. The rest of the track (e.g. 3/4) initially remains empty or with irrelevant data described. With several successive runs more and more areas of the track are described until finally the entire track is completely recorded.

In known methods lies between the Segment writes a phase of tape rewind in which for approx. 4 minutes (depending on transport speed and Tape length) no recording takes place, unless one Memory records this amount of data. At an input data rate of 8 Mbps and 4 minutes in duration, the memory should have a size of Have 1920 Mbit. Such a memory is too expensive for Consumer devices.

The helical-track magnetic tape recorder according to the invention has a bidirectional recording and playback operation with the tape feed speed in both directions  and is identical in both operating modes. The principle of segmented recording is applied. If in Forward transport direction the 1st segment has been recorded is and the end of the tape is reached, the tape run changes direction, and the 2nd segment with a changed track angle in Connection to segment 1 added. The through the Track angle difference occurring offsets of the track segments to each other through correspondingly large segment gaps caught. To buffer the response time of the drive There is a memory at the ends of the belt, the data for z. B. records 2 s.

The overall record consists of a series individual segmented individual records that are partially differ in their toe angle. Between the recording of the The belt running direction is switched over for individual segments. While of the switching processes, the data is buffered. The Segment length depends on the ratio of the input data rate to the recording data rate.

Segments that were written in the same direction of tape travel can be read simultaneously during a playback pass. The tracking information is obtained from only one segment. When recording, it becomes after a switching process filled memory until the next band direction switching process emptied. The memory is always filled up during playback kept to store data when changing direction to be able to provide.

The maximum record data rate is negligible on average higher than the input data rate. The playback data rate corresponds to the input data rate during recording. The Playback data rate is higher than the input data rate at Recording (when playing back multiple segments simultaneously). The data content of a single segment corresponds to the Audio or video information of a program.  

At the end of the tape, the drive is transferred to the inverse tape trans port direction and the operating and switch-off time point of the recording amplifier adjusted so that one to the previous written segment subsequent track segment with a another track angle is written.

The invention is explained below with reference to the drawing. Show in it

Fig. 1, 2, the segmented helical scanning of the tape,

Fig. 3, the head drum,

Fig. 4 shows the waveforms and

Fig. 5-7 constructive training for tape operation.

In Fig. 1 showing the segmented helical scanning for 4 segments S1-S4 of Bandunter- Bu to band upper edge Bo is depicted. Different hatches characterize the azimuth angles of the heads, which alternately (as shown) or in special versions write simultaneously. This angular offset effectively decouples neighboring track information when reading. It is recorded only in one tape running direction Bv. You must rewind between the recording of the individual segments. Gaps in the text ensure that the individual segments can be edited. B. are in the dubbing case. Such segment recordings are used in the 8 mm video system, at DAT and in the new digital video format DVC.

FIG. 2 shows the implementation of the segment position in two-way operation. The segments S1 and S3 have been recorded in one tape transport direction Bv, the segments S2 and S4 in the other. One group (S1, S3 or S2, S4) can be read in one run. The playback data rate in the case shown could therefore be twice as high as the recording data rate. The change in the writing track angle can be clearly seen. It is due to the inclined track recording. The legibility of the information of different track angles and thus extended functions (e.g. the display of all recorded programs) is strongly dependent on the segment length and the head width. The representation of the dashed lines L illustrates the reading limits for a track width of 10 µm and a track width of 14 µm.

To view the information in one direction during playback being able to read partially in the other direction becomes a defined one Phase offset observed during recording. For reference serve one or more already recorded segments. For this When inserting a new segment, the previous one is first written segment / s read and the new segment added accordingly.

Another solution is to add inverse letters Segments with variable phase offset, which arises automatically, if no phase synchronization measures are taken become. This operating mode only allows partial reading of information, but what a short program overview is quite sufficient.

Fig. 3 shows the head drum Kt with two 180 ° offset heads K1, K2, which have different azimuth angles. The belt B wraps around the head drum and is moved in both the indicated belt transport directions Bv.

In FIG. 4, from the rotation angular U (dipped at 0 ° head K1 in the tape a) are dependent and illustrated for the segmentation of the relevant signals. The blanking signal for the segment recording is obtained from a signal generator which is rigidly coupled in phase with the head drum. All gating intervals Ai for the write amplifier are shown, which were derived from the head drum servo. Only a limited number of them are selected by a logic per recording. The signals describing the tape are 1 D or 2 for the first pass. Run 2 D shown. The hatching corresponds again to the representations in FIG. 2.

The tracking information is stored in the data so that after writing a segment this when writing the next segment with the same track angle as a reference for tracking is used.

The reversal of direction of the belt transport Bv is through in the Sy stem existing data storage for 2 s uncritical and can e.g. B. through an interaction between the belt drive motor and Load motor carried out while avoiding belt loops become. Such switches are in the usual helical track recording devices (VHS, 8 mm) as play in the transition to review known. They are used for image search.

The fill level of the data memory in the system is at controlled the recording so that before a change of direction Memory content is minimal. The high level after the Rich Change of direction is reduced by a redundancy area which with different segment lengths or constant Realize segment lengths with nested dummy data. Both are possible. The redundancy size is negligible because on the smallest cassette with the longest playing time oriented, which can be accepted with 1 h. At a 6 Mbps input data rate, i. H. one saved Data volume of 12 Mbit, a redundancy of 0.05% is necessary.

Possible uses:

General for helical track magnetic tape recorders for digital data where the input data rate is lower than the record data rate, or at which data streams in discontinuous form. MPEG recorders Data streams. Data recording applications such as computer streamers based on DAT, 8 mm and DVC.

During playback, the memory is first filled, then the reading process begins. This ensures that at a continuous change of direction Data stream can be delivered.  

A further development is the advantageous implementation of a DVC Device with a season extension by a intermittent operation ("stop and go") with a special Device in the drive mechanism for noise and Reduce wear using the band jack motor for the winding plate drive is marked.

An inexpensive solution for a large number of is advantageous Dubbing without putting too much strain on the drive. The Ge noise level is low, and the track angle, bit length, etc. conforms to the specifications of the DVC standard.

The magnetic tape recorder works with full recording data rate (25 Mbps) and draws the data at an angle track down their information previously in a memory have been collected. If the memory is almost empty, the Recording process interrupted, the drive in the Playback mode brought, and with the help of Belt transport motor (operated inversely) in the previous taken shot positioned.

If the memory content approaches its maximum value, the Belt driving started, tracking was brought about and on the En the drive in the write to the previously written track was switched and a series of new tracks were written, until the memory is almost empty again. The data can later optionally with high data rate in continuous tape feed output (fast mode) or as with the recording in intermittent operation. There are two ways to do this available:

First: The request to transport the tape comes from Memory control and is thus from the collecting branch, e.g. B. the MPEG decoder determined.

Secondly, time stamps were stored on the tape, whose Evaluation of the drive operations as with the recording controls.  

The overall record consists of a series individual short records. Between the individual records drive operations are performed by the tape only drive motor are driven. The different moments will be of the coupling which is non-positively connected to the belt drive gene and brakes generated.

The short records are each at maximum data rate carried out. The maximum recording data rate is higher than the input data rate. The playback data rate corresponds to the Input data rate during recording. The playback data rate is higher than the input data rate during recording (to to the maximum recording data rate).

A data store adapts the input data rate and record data rate and buffers the drive responses ons times. The storage level controls the recording and tape transport cycle in recording and playback. In the Recording with recorded time reference marks controls the Tape transport cycle during playback. The belt drive motor drives the changing plate.

The following are exemplary embodiments of further training described.

The input data rate is constant 2 Mbps, the recording data 25 Mbps. With a memory of 64 Mbit depth and one the required reserve for 10/90% level detection is available Memory volume of 51.2 Mbit available, which is a record allowed for around 2 s. With a total recording time from 4 h 30 m on a cassette, this means a round 8000 times Settling and starting the tape transport. The rest period of the Drive (memory fill mode) is 25 s, although approximately 1 s must be deducted for the preparation of the new recording. Appropriate adjustments to other data rates or memory size ß are easily possible analogous to the given numerical values.  

From the above statements it can be seen that per cas frequently change the operating mode and direction must be in order to be able to use the long recording time. For consumer devices are directly driven changing plate systems, that switch quietly from home, for cost reasons Not insertable. With the new solution, is essential simplified drive complexity the same functionality reached. A low-noise drive switch is shown in the fol sections described. The mechanism uses the tape drive motor to reposition the tape.

The sequence is as follows:
The drive is initially in the recording mode, ie inclined tracks are written with the help of a rotating head drum with at least two heads, the track width resulting from the measure of the tape feed speed. In this mode, the previously with z. B. 2 Mbps filled data storage with z. B. 25 Mbps read out. If the level of the memory reaches the lower threshold (e.g. 10%), the write amplifier is switched off and the tape transport is stopped. During the memory filling phase that is now starting, the tape feed moves back a little and stops again. If the fill level of the memory reaches the upper threshold value (e.g. 90%), the playback mode moves to the end of the previously written area and switches to recording when the last written track is reached. A large number of new tracks are added until the memory reaches the lower fill level again. The write and read pointers of the memory are decoupled from one another. A so-called dual port memory can be used. A FIFO is also possible. It must then be ensured that the two pointers cannot "overtake" each other.

Fig. 5, 6 show the drive mechanics. The magnetic tape 1 wrapped around the head drum 2 is transported by the tape drive motor 4 and the pressure roller 3 via frictional connection. The winding plate slip clutches right 6 and left 10 are driven indirectly via belts 7, 8, 9 . Depending on the direction of rotation of the tape drive, the idler pivots to the right in standard playback mode or to the left in review mode (inverse direction at low speed). The tape tension of the respective winding plate receiving the tape is generated via slip clutches in the winding plates. In standard playback, the restraining band tension is generated by a band tension regulation consisting of brake band 11 , brake levers 12 , 13 and brake spring 14 . The brake band can be firmly clamped on one side ( FIG. 5) or be suspended on a movable brake band lever 17 ( FIG. 6).

The restraint belt pull in review mode is generated by a felt brake 16 . Depending on the direction of strip travel, the strip tension control 11 . . . 14 or the felt brake 16 are mutually brought into or out of function. A slide 15 or a corresponding element is usually used for this purpose. The elements mentioned can be found in many video recorders these days. They can be manufactured inexpensively and have also proven themselves in rough use.

The change in operating mode between normal reproduction and review and the movement of the slide 15 by the tape transport motor is related to the fact that a torque is made available in the central clutch 7 , so that this moment on the idler lever 8 or an additional lever (not shown) from the slide 15 can be removed.

Through this particularly low-noise and endurance-resistant type of It is not brake control (indirect brake operation) required another motor and a cam during normal playback and review switching ern.

FIG. 7 shows a modification of the drives of FIGS. 5 and 6, which, apart from the main brakes for fast rewinding, gives an example of all further drive functions.

Furthermore, a slip clutch 19 is shown, which provides a moment that can be removed from the slide 15 on the pin 20 .

In the embodiment of Fig. 7, a tension spring has been added 18. Like the brake band 11, it acts on the brake lever 17 . Both forces should cancel each other and thus relieve the slide 15 . The slip clutch 19 can be dimensioned correspondingly weak, which in turn relieves the belt drive motor 4 in the play review mode.

In order to make the horizontal formwork movement of slider 15 as smooth as possible, universal joint bearings are provided on pendulum supports.

The switching of the drive function, which are not caused by the drive motor 4 at Bandan, are positively controlled. To do this, some bearing points must be movably arranged. They can be moved to position a, b or c, each corresponding to a drive mode.
a = tape loading, ie threading magnetic tape into or out of the drive
b = play review, these are all fashion with the pressure roller 3 pressed on
c = wind-rewind, belt drive through the winding plate slip clutch 6 , 10 , which are bridged in this operating mode.

Possible uses:

General for helical track magnetic tape recorders for digital data where the input data rate is lower than the record data rate. The data must be on average be constant, but can (depending on memory size) in short Time intervals differ significantly. MPEG recorders Data streams. Data recording applications such as computer streamers based on DAT, 8 mm and DVC.

Claims (8)

1. A method for recording a digital signal, characterized in that the overall record consists of a series of individual segmented individual recordings gene, which differ in their track angle or that the overall record consists of a series of individual short records, all of which have the same track angle. 2. The method according to claim 1, characterized in that between the recording of the individual segments Belt direction switched and / or during the changeover operations the data are cached and / or the Segment length depending on the ratio of the input data rate to the recording data rate. 3. Method according to one or more of the preceding Claims, characterized in that segments which in same tape direction were written simultaneously at a playback pass can be read and / or the Tracking information is obtained from only one segment and / or when recording the after the switching process filled memory until the next band switchover and / or the memory is always filled during playback held, and when changing direction from memory Data will be provided. 4. Method according to one or more of the preceding Claims, characterized in that between the Single records drive operations are performed which are only driven by the belt drive motor and / or the different moments of with the belt drive frictionally connected clutches and brakes become. 5. Method according to one or more of the preceding Claims, characterized in that the short records  are each carried out at the maximum data rate and / or the maximum recording data rate higher than that Input data rate is. 6. Method according to one or more of the preceding Claims, characterized in that the Playback data rate of the input data rate at the Record corresponds and / or the playback data rate is higher than the input data rate when recording maximum recording data rate. 7. Method according to one or more of the preceding Claims, characterized in that a data memory Adaptation between input data rate and Record data rate makes and the drive freak buffer times and / or the storage level Recording and tape transport cycle for recording and Playback controls and / or when recording with recorded time reference marks the tape transport of the Control the cycle during playback and / or the Belt drive motor drives the winding plate. 8. Recorder for a recording method according to one or more of the preceding claims, characterized in that the magnetic tape ( 1 ), the head drum ( 2 ), the pressure roller ( 3 ), the tape drive motor ( 4 ), the belt ( 5 ), winding plate slip clutch ( 6 ), central clutch ( 7 ), the idler lever ( 8 ), the idler wheel ( 9 ), wind-up slip clutch on the left ( 10 ), brake band ( 11 ), brake lever ( 12 ), band tension sensor ( 13 ), brake spring ( 14 ), slide ( 15 ), felt brake ( 16 ) and brake band lever ( 17 ) are parts of the recorder.