JPH03269818A - Detecting method for wear of magnetic head - Google Patents

Abstract

PURPOSE:To detect the worn state of a head targeted to be detected by studying the change pattern of reproducing output in one or plutal times of still recording and reproduction based on the self-recording or reproduction of the head in a state where the feed of a magnetic tape is stopped. CONSTITUTION:When the feed of the magnetic tape(MT) is stopped, the still recording in first rotation is still-reproduced by scanning with the head A during 1/4 rotation when the head A scans the MT, and a reproducing voltage in a coil 8a generated by the still reproduction is inputted to a reproducing amplifier 9 via switches 6, 5, and a reproducing signal proportional to the reproducing voltage is outputted to a switch 11. The signal is inputted to a level detection circuit 13, and detection data is outputted to a control detection processing circuit 14. The circuit 14 detects the change pattern of the reproducing output of the head A, and compares it with the change pattern that is detection reference stored in advance, thereby, the automatic detection of the worn state of the head A can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a rotating head type magnetic recording/reproducing apparatus such as a VTR or R-DAT, and more particularly to a method for detecting wear of a magnetic head attached to a rotating cylinder.

(B) Prior Art Conventionally, in an R-DAT, a pair of magnetic heads attached to a rotating cylinder alternately helically scans a running magnetic tape to perform recording or reproduction. In such a helical scan type device, the relative speed between the magnetic tape and the magnetic head is very high, so the magnetic head wears out over long periods of use. When the magnetic head wears out, the so-called head depth decreases, the optimum recording current value of the magnetic head decreases, and the frequency characteristics during recording and reproduction change, making it impossible to perform good recording and reproduction. Therefore, it is necessary to detect the wear status of the magnetic head and adjust or replace the magnetic head as necessary. That is, in order to detect the wear status of the magnetic head without removing the magnetic head from the R-DAT, conventionally a large and special microscope device (jig) was used to observe the amount of protrusion of the magnetic head from the rotating cylinder. However, in addition to this observation, the state of wear of the magnetic field is also detected.

(c) Problems to be Solved by the Invention The above-described magnetic head wear detection method requires a large and special device such as a microscope for detection, and also requires complicated operations and requires a skilled worker. There is a problem that accurate detection cannot be performed unless the person is a person.

In addition, Japanese Patent Application Laid-open No. 109602/1983 (GlI B
5/46), a plurality of measurement signals of different frequencies are sequentially generated at a predetermined period and recorded by a magnetic head, and then the recorded measurement signals are reproduced by the magnetic head to detect the level. However, since the frequency of the measurement signal is discontinuous, there was a problem with accuracy.

B) Means for Solving the Problems The present invention is intended to solve the above problems, and provides a method for detecting wear of a magnetic head of a rotating head type magnetic recording/reproducing device. At the same time, the running state of the magnetic tape is controlled to stop or be in an intermittent drive state, and static recording and playback of the head to be detected is performed at one time.
times, or multiple times, during one static recording, or once
A recording current of a constant level whose frequency changes continuously for each static recording is supplied to the detection target head during recording, and the detection target is determined based on the change pattern of the playback output obtained by static reproduction of the detection target head. This invention proposes a magnetic head wear detection method characterized by detecting head wear.

(e) Effect: According to the above means, the wear of the head to be detected can be detected by controlling the playback output of one or more static recording/playback operations in order to enable the head to perform self-recording and playback when the magnetic tape has stopped running. It can be detected by changing patterns.

(F) Embodiment Next, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

Figure 1 shows the blocks when applied to R-DAT. In the figure, (1) is a recording input terminal into which a PCM signal for normal recording is input, and (2) is a recording input terminal that is input with a frequency control signal to be described later. A test signal generator whose frequency is varied at a constant level, (3) is a recording signal changeover switch that is switched by an input/output selection signal described later, and has two contacts (i)
(i') to switch the PCM signal from the input terminal (1) or the test signal from the generator (2). (4) is a recording amplifier into which the signal from the changeover switch (3) is input; (5) is a recording/reproduction changeover switch which is changed over by a recording/replay changeover signal described later; It is input to the contact (r). (6) is a head changeover switch that is changed over by a head changeover signal to be described later; a changeover piece is connected to the changeover piece of switch (5), and contacts (a) and (b) are connected to a rotary cylinder via a rotary transformer (7). The head coil (8
a) (8b) are connected to each other. (9) is a reproduction amplifier to which the reproduction voltage of the reproduction contact (P) of the switch (5) is input, which amplifies the input voltage and outputs a reproduction signal having a voltage level proportional to the input voltage. (10) is a reproduction equalizer circuit that equalizes the waveform of the reproduction signal of the amplifier (9) and outputs the same; (11) is a reproduction signal changeover switch that is switched together with the switch (3) by an input/output selection signal; Output the reproduction signal of (1o) from the reproduction output terminal (12) through the contact (o),
Alternatively, the reproduced signal is switched and outputted to a level detection circuit (13) to be described later through a contact (0'). Reference numeral (13) denotes a level detection circuit to which a reproduced signal is input via the contact (0') of the switch (11) when wear is detected, and outputs detection data of the detected level.

(14) is a control detection processing circuit consisting of a microcomputer, which stores in advance a control program during normal recording/reproduction and a control/detection processing program during wear detection, and switches the switches (3) and (11). input/output selection control signal (Sa) for the test signal generator (2), frequency control signal (Sb) for the test signal generator (2), recording/reproduction switching signal (Sc) for switching the switch (5), It forms and outputs a head switching signal (Sd), and also includes a rotation control mechanism,
It has a mechanism control function for controlling the running of the magnetic tape and a detection processing function for automatically detecting the state of wear from the detection data of the level detection circuit (13) and determining the degree of wear.

In addition, based on the R-DAT standard, a pair of magnetic heads are installed on a rotating cylinder 180 degrees apart, and the magnetic tape is wound around the rotating cylinder with a 90" winding and runs. Then, the switches (3) (11) ) is the control signal (Sa
), one contact (
i) (o), and when magnetic head wear is detected, the contacts are switched to the other contacts (i') (o'). In addition, the recording/reproduction changeover switch (5) is operated based on the changeover signal (Sc).
It is switched in response to the recording/playback switching operation during normal recording/reproduction, and is automatically switched when magnetic head wear is detected. Furthermore, the head changeover switch (6) receives a changeover signal (
(Sd), the contact is switched every half rotation of the rotating cylinder during normal recording and playback, and when magnetic head wear is detected, it is switched to either contact (a) or (b) and held according to the designation of the head to be detected. Ru. On the other hand, test signal generation 5
(2) operates as a variable frequency signal with a constant level when magnetic head wear is detected based on the control signal (Sb).

Further, the magnetic tape is controlled by the above mechanism to run at a constant speed during normal recording and reproduction, and is controlled to stop running when magnetic head wear is detected.

Furthermore, since the rotating cylinder always rotates at a constant speed during normal recording/reproducing and when detecting magnetic head wear, both magnetic heads always rotate at a constant speed. During normal recording, the PCM signal for recording at the input terminal (1) is input to the recording amplifier (4) via the recording signal changeover switch (3), and from the amplifier (4) to the recording/reproduction changeover switch ( A recording current corresponding to the PCM signal for recording is output to the head changeover switch (6) via the head changeover switch (5). By the way, the magnetic tape is 90"
Since the magnetic tape runs by winding, both magnetic heads scan the magnetic tape only while the rotary cylinder rotates 1/4 (=90°). Based on the switching signal (Sd), the head switching switch (6) is switched in synchronization with the rotation of the rotary cylinder, and one magnetic head (hereinafter referred to as A head) is switched.
During 174 rotations when the magnetic tape is scanned, the recording current of the switch (5) is supplied to the coil (8a) of the A head via the switch (6) and the rotating transformer (7).
During 174 rotations when the other magnetic head (hereinafter referred to as the B head) scans the magnetic tape, the recording current of the switch (5) passes through the switch (6) and the transformer (7) to the coil (8b) of the B head. ), and a PCM signal for recording is recorded on the magnetic tape in a helical scan manner. Also, during normal playback, the playback voltages of the coils (8a) and (8b) generated by the scanning of the A and B heads are input to the amplifier (9) via the switches (5) and (6). ) outputs a PCM signal reproduced from the magnetic tape to the switch (11) via the equalizer circuit (10). Since the switch (11) is switched to the contact (o) based on the control signal (Sa), the PCM signal waveform-equalized by the equalizer circuit (10) is passed through the switch (11) to the output terminal (12).
) is output.

Next, the operation when detecting wear of the magnetic head will be explained.

First, the magnetic tape is stopped running, and one of the heads to be detected is
The wear status of the head is detected by static recording and reproducing. Therefore, when wear is detected, the running of the magnetic tape is controlled to stop by the mechanical control of the control detection processing circuit (14) based on the wear detection setting operation, and the recording/reproduction switch (5) is rotated based on the changeover signal (Sc). It is switched to contact (r) during the first rotation of the cylinder at the start of detection. In addition, by specifying which of the A and B heads is the head to be detected by the head selection operation, the control signal (Sd
), the head changeover switch (6) is switched to and held at the contact point of the head to be detected. Further, by performing a detection start operation, the test signal of the generator (2) is outputted to the contact (i') of the recording signal changeover switch (3).

By the way, the self-recording and reproducing characteristics of the magnetic tape by the A and B heads change depending on the wear condition of the head, and as shown by the solid line A and the dashed-dotted line B in Fig. 2, the frequency characteristics change depending on the wear condition. do. The greater the wear, the higher the low range and the steeper the high range. Note that the solid line A in FIG. 2 shows the characteristics with respect to the recording frequency when there is no wear, and the dotted chain line B shows the characteristics with respect to the recording frequency when there is large wear.

If the running of the magnetic tape is stopped, the recording frequency is changed, and the head to be detected performs self-recording and playback, the effects of fluctuations in the running of the magnetic tape can be eliminated, and the wear of the head to be detected can be reduced. A corresponding variation pattern of the playback output can be obtained. Based on the control signal (Sb), the test signal generator (2) is then continuously varied, for example from a low frequency to a high frequency, during 174 revolutions of the rotary cylinder during which the magnetic tape is scanned.

Then, when the A head is specified as the head to be detected and a detection start operation is performed, the recording/reproduction changeover switch (5) is switched to contact (r) during the first rotation of the rotating cylinder, and the recording is controlled. Therefore, the test signal of the generator (2) is transferred to the recording amplifier (4) via the recording signal changeover switch (3).
input from the recording amplifier (4) to the switch (5),
A recording current is supplied to the A head coil (8a) through the coil (6), and the magnetic tape is statically recorded by the A head. At this time, the recording frequency supplied to the head coil (8a) by the frequency control of the test signal generator (2) based on the control signal (Sb) is as shown in Fig. 3, which shows the time change of the recording/reproduction signal of the A head. As shown in the waveform (R), the frequency changes continuously from low frequency to high frequency during 1/4 rotation when the A head scans the magnetic tape. Then, when the first revolution of the rotating cylinder is completed and the next revolution begins,
The recording/reproducing switch (5) is switched to the contact (P) by the switching signal (Sc) to control playback, and at this time, since the magnetic tape has stopped running, the A head scans the magnetic tape (174). During the rotation, the A-head accurately scans the static record of the first revolution and reproduces it statically, and the coil (8
The reproduction voltage of a), for example, the reproduction voltage of the waveform (P) in FIG. 3, is applied to the reproduction amplifier (
9), and a reproduction signal proportional to the reproduction voltage is outputted from the amplifier (9) to the switch (11) via the reproduction equalizer circuit (10). Further switch (11)
The reproduced signal is input to the level detection circuit (13), and from the detection circuit (13), the detection data formed by sampling and holding the voltage level of the reproduced signal and digitally converting it is sent to the control detection processing circuit (14). Output. Then, the control detection processing circuit (14) detects a change pattern in the reproduction output of the A head obtained by static reproduction based on all the detection data inputted based on the operation of the detection processing function, and also detects, for example, The change pattern is compared with one or more change patterns of detection standards stored in advance, and the wear status of the A head is automatically detected from the comparison result. In addition, automatic detection of the wear condition allows control and
Based on the detection result, the detection processing circuit (14) selectively lights up, for example, a plurality of light emitting diodes for wear display provided in the display section to display the wear status of the A head.

By the way, when the B head is designated as the detection target and the detection start operation is performed, the head changeover switch (6) is switched to the contact point (b) corresponding to the B head and held, except that the above-mentioned A head The wear condition of the B head is detected in the same manner as in the case of the above case.

Therefore, in the above-mentioned embodiment, the head to be detected automatically performs one self-recording and reproducing operation when the magnetic tape stops running, and performs one static recording and reproducing operation. The wear status of the target head is automatically detected electrically based on the pattern of changes in the playback output of the target head, and wear can be easily detected with simple operations without the need for large and special detection equipment (jigs) such as microscope equipment. The situation can be detected with high accuracy. In addition, since detection is performed only by one static recording and playback, it is possible to detect quickly in a very short time of only two rotations of the rotating cylinder, and the length of the magnetic tape required for detection is short. fast, economical detection. Furthermore, by incorporating the configuration shown in FIG. 1 into the R-DAT set, the user of the set can detect and know the wear status at any time, and can perform ideal head management. For example, the rotary transformer (7) in Fig. 1, the head coil (
Even if each part except 8a) and (8b) is installed in a separate detector from the R-DAT set, the wear status can be detected by switching the connection between the circuit in the set and the detector only at the time of detection. good.

Incidentally, in the embodiment described above, the wear status of the magnetic head is detected by one static recording/reproducing operation, but it is also possible to detect the magnetic head wear status by multiple static recording/reproducing operations as described below. That is, when detecting wear, the magnetic tape is controlled to be driven intermittently, and the tape position scanned by the head to be detected is shifted every time required for one stationary recording/playback, and once during each run of intermittent drive. At the same time, for each static recording shown in Figure 1, the test signal generator (2)
The frequency of the signal is varied from low frequency to high frequency and is supplied to the detection head. Furthermore, the average value of each reproduction output obtained by each static reproduction is determined, and the wear status of the head to be detected is detected from the change pattern of the average value.

Therefore, when the wear condition is detected by static recording and reproducing multiple times as described above, there is an advantage that the detection can be performed with high precision and stability.

It is also possible to detect dirt on the head. When the head becomes dirty with dust etc., the line B in Figure 3
As in, the high range drops sharply. By detecting this characteristic with the control detection processing circuit (14), it is possible to know whether the head is dirty.

It goes without saying that the present invention is applicable to various rotary head type magnetic recording and reproducing apparatuses such as video tape recorders other than R-DAT.

(g) Effects of the Invention As described above, according to the magnetic head wear detection method of the present invention, the wear status of the detection target head can be detected by detecting the change in the reproduction output of the detection target head. It is possible to accurately detect wear conditions in a short time with simple operations without using large and special equipment such as conventional microscope equipment, and the magnetic head in rotating head type magnetic recording and reproducing devices such as R-DAT. extremely useful for detecting wear conditions.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an R-DAT device that employs the magnetic head wear detection method of the present invention, and FIG. 2 is a diagram showing the relationship between recording frequency and reproduction output in the detection method of the present invention.
FIG. 3 is a waveform diagram showing the operation of the magnetic head in the detection method of the present invention. (2)...Test signal generator, (3)...Recording signal selection switch, (11)...Reproduction signal selection switch, (
13)... Level detection circuit, (14)... Control/detection processing circuit.

Claims (1)

[Claims] 1) In a method for detecting wear of a magnetic head of a rotary head type magnetic recording/reproducing device, the head to be detected is fixed in a recording/reproducing state, and the running state of the magnetic tape is stopped or in an intermittent drive state. The head to be detected is controlled to perform static recording/reproduction once or multiple times, and a recording current of a constant level whose frequency changes continuously during one static recording or for each static recording is applied to the recording current. A method for detecting wear on a magnetic head, characterized in that wear of the head to be detected is detected from a change pattern of reproduction output obtained by static reproduction of the head to be detected, which is supplied to the head to be detected.