JPH05234043A - Method for measuring projecting quantity of rotary magnetic head - Google Patents

Abstract

PURPOSE:To safely and surely measure the wear quantity of the rotary head of a VTR in a use state. CONSTITUTION:A standard tape 2S recorded with at least first and second mark signals respectively in the positions different from each other on magnetic tracks is reproduced by a rotary magnetic head 1 before the use of this rotary magnetic head 1 is started. The time interval Ti of the first and second mark signals Ms, Mf obtd. at the time of this reproduction is measured and the result of the measurement is stored into a memory 24. The standard tape 2S is reproduced by the rotary magnetic head 1 after the use of the rotary magnetic head 1. The time interval Tw of the first and second mark signals Ms, Mf obtd. at the time of this reproduction is measured. The projecting quantity after the use of the rotary magnetic head 1 is measured in accordance with the result of this measurement and the result of the measurement previously stored into the memory 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the amount of protrusion of a rotary magnetic head in a VTR or the like.

[0002]

2. Description of the Related Art In a helical scan type VTR, a rotary magnetic head records and reproduces a video signal on a magnetic tape, for example, as one oblique magnetic track for each one field. During playback,
The rotating head inevitably wears as it rotates while contacting the tape. Then, as the wear of the rotary head progresses, the magnitude of the optimum recording current changes, the high-frequency level of the reproduction signal lowers, and other problems occur in recording and reproduction. Therefore, generally, the guaranteed time (usable time) of the rotary head is estimated to be, for example, 1000 hours, and
When R is used for the guaranteed time, the rotary head is replaced. Alternatively, it is considered that the rotary head can be used as it is within the guaranteed time.

However, due to various factors, some rotary heads have little wear even after the guaranteed time has been used, and some rotary heads have abnormal wear even if they do not meet the guaranteed time. Therefore, the rotary heads are replaced according to the guaranteed time. If so, trouble may occur in recording or reproduction, and in the worst case, recording or reproduction may not be possible.

Therefore, a jig for measuring the amount of protrusion of the rotary head has been developed. This is because if the rotary head wears,
Since the amount of protrusion of the rotary head from the head drum (rotary drum) also decreases in proportion, the amount of wear of the rotary head can be measured by measuring the amount of protrusion.

[0005]

However, since the projection jig for measuring the amount of protrusion is designed to be brought into direct contact with the tip of the core of the rotary head, the rotary head is damaged during measurement. There is a risk of damage and scratches. Further, since it is a contact type, it is necessary to remove the exterior of the VTR at the time of measurement, and there is also a problem that the measurement cannot be easily performed in a place where the VTR is used.

The present invention solves the above problems and provides a measuring device capable of safely and reliably measuring a change in the protrusion amount of a rotary head due to wear under the condition of use. Is what you are trying to do.

[0007]

Therefore, in the present invention, the details of which will be described later, the form of the magnetic track will be reviewed anew, and based on the result of the examination, the amount of protrusion or wear of the rotary head will be increased by signal processing. This is to make it possible to know the quantity.

That is, when the reference numerals of the respective parts correspond to the embodiments described later, the rotary magnetic head 1 records or reproduces an information signal in a predetermined amount on the magnetic tape 2 as an oblique magnetic track. In measuring the protrusion amount of the rotary magnetic head 1, at least the first
And the second mark signals Ms and Mf indicate that the magnetic track Tk
The reference tapes 2S recorded respectively at different positions on i are reproduced by the rotary magnetic head 1 before the use of the rotary magnetic head 1, and the first tape obtained at the time of the reproduction is reproduced.
Also, the time interval Ti between the second mark signals Ms and Mf is measured, the measurement result is stored in the memory 24, and after the use of the rotary magnetic head 1, the reference tape 2S is reproduced by the rotary magnetic head 1 and this reproduction is performed. The time interval Tw between the first and second mark signals Ms and Mf obtained at times is measured, and based on this measurement result and the measurement result stored in the memory 24, the rotary magnetic head 1 after use is measured. The amount of protrusion is measured.

[0009]

The change in the protrusion amount of the rotary head 1, that is, the wear amount is measured by the signal processing. Therefore, VT
It is possible to perform the measurement safely and surely while the R is being used.

[0010]

The present invention is based on the following facts. That is, when the rotary head is worn, the effective rotational diameter of the rotary head is reduced, but even if the effective diameter is reduced in this way, a step (tape of the tape) between the lead-in side and the lead-out side of the head drum is reduced. The width occupied by the video track does not change in the width direction. Therefore, when the rotating head is worn, compared to when it is not worn,
It is based on the knowledge that the length of the recorded video track (the length of the scanning section at the time of reproduction) becomes short and the tilt angle becomes large.

First, the change in the length of the video track and its inclination angle due to wear of the rotary head will be described with reference to FIGS.

In FIG. 5, a broken line indicates a state where the rotary magnetic head is not worn, a solid line indicates a worn state, 1 is a rotary magnetic head, 2 is a magnetic tape, and 3 is a head drum. The head 1 is shown at angular positions every 90 °. Further, the rotation direction (scanning direction) of the head 1 and the running direction of the tape 2 are the same. Further, FIG. 6 shows a tape running path of the drum 3. Further, FIG. 7 shows the track pattern in the initial state, and Tki is its video track. The solid line in FIG. 8 shows the track pattern when the head 1 is worn (the broken line is the same as in FIG. 7), and Tk
w is the video track.

Then, as shown in FIG. 5, the protrusion amount of the head 1 is a normal value Pi, and the effective diameter of the drum 3 is a value D.
Even when the head 1 is worn by the value ΔP from the state of i and the effective diameter of the drum 3 is reduced to the value Dw (= Di−2ΔP), the winding angle α of the tape 2 with respect to the drum 3 is
It does not change mechanically. Further, as shown in FIG. 6, the step H between the lead-in side and the lead-out side of the drum 3 does not change mechanically. The occupied width Wv of the video tracks Tki and Tkw in the width direction of the tape 1 is equal to the step H, which does not change even when the head 1 is worn.

Therefore, as shown in FIG. 7 and FIG.
When the head 1 is worn, the length of the video track is shortened from the initial length Li to the length Lw, and the still angle corresponding to the lead angle is increased from the initial angle θoi to the angle θow. The inclination angle of the track also increases from the initial angle θri to the angle θrw.

On the other hand, the video track on the tape 1 is formed by vector synthesis of the running of the tape 1 and the rotation of the rotary head 2. Therefore, tape speed is Vt, head 1
Assuming that the rotation cycle of the head 1 is Td, as shown in FIG.
While the tape 2 moves by the distance VtTd, the head 1 moves by the distance πDi, and the video track TKi having the inclination angle of θri is formed. Further, when the head 1 is worn, the tape 2 is separated by the distance VtT as shown in FIG.
While moving by d, the head 1 moves by a distance πDw, and a video track TKw having an inclination angle of θrw is formed.

Then, in the initial state of the head 1, the length Ls of the still track when only the head 1 moves.
i is as follows, where the winding angle of the tape is α radian (see FIG. 5). Lsi = πDi × α / 2π = αDi / 2 Further, the time for the head 1 in the initial state to scan the length Lsi of the still track, that is, the initial recording time Ti.
Is as follows. Ti = Td × α / 2π On the other hand, according to FIG. 7, in the initial state of the head 1,
The following relationship is established between the length Li of the video track TKi and the movement amount of the head 1 and the tape 2 (x ** y represents x to the power y). (2πLi / α) ** 2 = (πDi cos θoi−VtTd) ** 2+ (πDi sin θoi) ** 2 = (πDi) ** 2+ (VtTd) ** 2 −2πDiVtTd cos θoi ∴ Li = (α / 2π) {(ΠDi) ** 2+ (VtTd) ** 2 −2πDiVtTd cos θoi} ** (1/2) That is, when the head 1 is in the initial state, the period T
When a recording current is passed by i, a video track T of length Li
It shows that ki is formed. Alternatively, the length L
When playing the video track Tki of i, the time T
It indicates that i is required.

Similarly, when the head 1 is worn, as shown in FIG. 8, the following relationship is established between the track length Lw and the movement amount of the head 1 and the tape 2. (2πLw / α) ** 2 = (πDw cosθow−VtTd) ** 2+ (πDw sinθow) ** 2 = (πDw) ** 2+ (VtTd) ** 2 −2πDwVtTd cosθow Then, in the above equation, If the relationship between the initial recording time Ti and the winding angle α is substituted and arranged, the track length Lw when the head 1 is worn can be expressed as follows. Lw = (Ti / Td) {(πDw) ** 2+ (VtTd) ** 2 −2πDwVtTd cos θow} ** (1/2) (i) That is, in the above equation, the head 1 is worn. In the state, when the recording current is supplied for the period Ti, the track Tk having the length Lw is obtained.
It shows that w is formed. It also indicates that time Ti is required when reproducing the video track Tkw having the length Lw.

Since the lead step H of the drum 3 (see FIG. 6) is constant regardless of the wear of the head 1 as described above, each still angle in the initial state and the worn state of the head 1 is different. The following relationship is established between θoi and θow. θow = arctan {(Di / Dw) tan θoi} Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 4. In FIG. 1, reference numeral 10 denotes a VTR reproducing system, for example, two rotary magnetic heads 1 and a drum 3
Are arranged with an angular interval of 180 ° and are rotated at a period Td. Further, the magnetic tape 2 is made to travel obliquely with respect to the rotating peripheral surface of the head 1 over an angular range of a little over 180 °. A video signal is recorded on the tape 2, for example, as one oblique magnetic track per field.

Thus, at the time of general reproduction, the head 1 alternately reproduces the video signal from the tape 2, and the reproduction signal is supplied to the reproduction signal processing circuit 14 through the switch circuit 12 and the reproduction equalizer circuit 13. Video signal is taken out.

Reference numeral 20 denotes a protrusion amount measuring circuit, which has a microcomputer 21 and a counter 22, to which the output of the equalizer circuit 13 is supplied as a count control signal. A clock is supplied as a count input from the pulse generation circuit 23, and the count output is supplied to the microcomputer 21. Further, the microcomputer 21 has
The non-volatile memory 24 and the display means 25 are connected.

In the present invention, the amount of protrusion of the head 1 is measured based on the above-mentioned findings regarding changes in the track length and the inclination angle due to wear of the rotary head 1. Then, the reference tape 2S for measurement is manufactured by the VTR in which the protrusion amount of the rotary head is controlled to the regular value P.

That is, for example, as shown in FIG. 3, in the standard tape 2S, one video track Tki is formed obliquely with respect to the tape 2S, like the video track in the general tape 2, and The mark signals Ms and Mf for measurement are recorded at a plurality of predetermined positions on the track TKi, for example, at the start end and the end. Therefore, the mark signals Ms and Mf have time intervals Ti corresponding to the start and end of the track TKi,
The timing needs to be synchronized with the rotation of the head and the drum, but there is no special limitation on the frequency or waveform, and a specific signal at the start and end of the reproduced video signal for one field is used. You can also It is also possible to use signals at a plurality of predetermined positions other than the start end and the end on the track Tki.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. 2 and 4.

As shown in FIG. 2, before starting the operation of the VTR, that is, in the initial state of the rotary head 1, the reference tape 2 is used.
S is reproduced (step 31). Then, when the head 1 reproduces the track Tki, the mark signal Ms,
Although Mf is reproduced (FIG. 4A), the signal Ms allows the counter 22 to count and the signal Mf prohibits the counter 22 from counting. Thus, the clock (FIG. 4B) from the pulse generator 23 between the signal Ms and the signal Mf is counted, and the time interval Ti between the signal Ms and the signal Mf is measured (step 32). Is written in the memory 24 as an initial value (step 33).

After that, the VTR is operated as usual, and recording and reproduction of the tape 2 are performed. Moreover, the head 1 is gradually worn by this operation.

Then, for example, at the time of periodical inspection,
The standard tape 2S is reproduced (step S41), and the time interval Tw between the mark signal Ms and the signal Mf is measured in the same manner as described above (step 42).

In this case, when the video track Tki is reproduced with the rotary head 1 worn as described above, the length of the video track TKi that can be reproduced at the time Ti is a value Lw shorter than the track length Li. From the worn head 1 to the video track Tki (length Li)
The time Tw required to reproduce the data is longer than the time Ti. Then, with the head 1 in this worn state, the time T
The length Lw of the track Tki that can be reproduced on i is expressed as follows. Lw = Li × Ti / Tw (ii) Then, the measured value Ti in the initial state is read from the memory 24 (step 43), and then the measured values Ti and Tw before and after the operation.
Based on the above, the track length Lw at the time of head wear is calculated by the formula (ii), and the effective diameter Dw of the drum 3 that achieves this track length Lw is calculated by the formula (i), and the The protrusion amount or wear amount of the head 1 is calculated (step 44), and this protrusion amount or wear amount is displayed on the display means 25 (step 45).

In the above description, the rotational direction (scanning direction) of the head 1 and the traveling direction of the tape 2 are the same, but in the opposite case, the equation (i) is Lw = ( Ti / Td) {(πDw) ** 2+ (VtTd) ** 2 + 2πDwVtTd cos θow} ** (1/2).

In the above description, the number of rotary heads is one pair, but even when a large number of rotary heads are used, the present invention can be similarly applied to each rotary head, and individual rotary heads can be used. The amount of head wear can be measured at the same time.

Furthermore, the present invention can be applied to any device that records or reproduces information signals using a rotary head such as R-DAT, not limited to VTRs. Further, by knowing the protrusion amount of the rotary head, it is possible to automate the adjustment of the recording current and the adjustment of the recording frequency characteristic in the case of the recording head, and the adjustment of the reproducing frequency characteristic in the case of the reproducing head. Can be automated.

[0031]

As described above, according to the present invention, the reference tape 2S on which the mark signals Ms and Mf are recorded is prepared on the track Tki, and the reference tape 2S is measured by the rotary head 1 to be measured. The time interval Ti between the mark signals Ms and Mf before reproduction is regenerated before and after use.
The mark signals Ms, M after the start of use.
The time interval Tw of f is measured, and the wear amount Δp of the measured magnetic head 1 is calculated based on these measured values Ti and Tw.

Therefore, according to the present invention, when the wear amount ΔP of the magnetic head 1 is measured, the head 1 is not damaged or scratched and can be measured safely and reliably. You can Also, at the time of measurement, it is not necessary to remove the exterior of the VTR,
It can be easily measured.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of the present invention.

FIG. 2 is a flowchart showing the operation of an example of the present invention.

FIG. 3 is a diagram of a track pattern for explaining the present invention.

FIG. 4 is a waveform diagram for explaining the operation of the present invention.

FIG. 5 is a plan view for explaining the present invention.

FIG. 6 is a perspective view for explaining the present invention.

FIG. 7 is a diagram of a track pattern for explaining the present invention.

FIG. 8 is a diagram of a track pattern for explaining the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rotating magnetic head 2 magnetic tape 2S standard tape 3 head drum 10 reproducing system 21 microcomputer 22 counter 23 clock generation circuit 24 non-volatile memory

Claims (1)

[Claims] 1. An apparatus for recording or reproducing an information signal in a predetermined amount on a magnetic tape as a slanted magnetic track by a rotary magnetic head, wherein at least the amount of protrusion of the rotary magnetic head is measured. The standard tapes in which the first and second mark signals are recorded at different positions on the magnetic track are reproduced by the rotary magnetic head before the use of the rotary magnetic head. The time interval between the first and second mark signals is measured, the measurement result is stored in a memory, and after the rotary magnetic head is used, the standard tape is reproduced by the rotary magnetic head. The time interval between the first and second mark signals is measured, and based on the measurement result and the measurement result stored in the memory, the time A method for measuring the amount of protrusion of a magnetic head, which measures the amount of protrusion of the magnetic head after use.