JPH0471241B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an erasing device for a magnetic recording or reproducing device, and in particular to an erasing device that is capable of erasing only one track of magnetic signals recorded over a large number of tracks. The goal is to find a way to erase the data without adversely affecting subsequent recording or playback. Prior Art In a magnetic recording or reproducing device, such as a VTR,
When editing recording information, it is necessary to erase one video track at a time, rather than erasing the entire width, in order to connect the editing points neatly without disturbing the image. Furthermore, when it is desired to rewrite only one track of information recorded over a large number of tracks on a rotating disk-shaped recording medium such as a magnetic disk or magnetic sheet, it is necessary to erase only one track in the same manner as described above. Conventionally, in order to erase only one track, a head similar to a recording or reproducing head has been used and an alternating current or direct current magnetic field is used for erasing. However, in order to obtain a sufficient erasing rate, it is necessary to apply a sufficiently large erasing magnetic field, which necessitates increasing the gap width of the head. However, when the gap width is increased, the peripheral magnetic field generated from the side surfaces of the gap also becomes larger, causing a phenomenon in which adjacent tracks are excessively erased, and this effect becomes more pronounced as the track spacing becomes narrower. Therefore, the erase gap cannot be made too large, but if it is made small, a sufficient erase magnetic field cannot be obtained, and furthermore, the magnetic field where recorded magnetization occurs before erasing is recorded at the trailing edge of the erase gap. The so-called re-recording effect (see material MR-79-10 of the Magnetic Recording Study Group of the Institute of Electronics and Communication Engineers) becomes noticeable, and in any case there is a drawback that a sufficient erasure rate cannot be obtained. In order to improve the erasing rate, it is conceivable to operate the erase head multiple times and repeatedly apply the erase magnetic field to the track to be erased, but this would complicate the operation, lengthen the erasing time, and increase power consumption. Therefore, it is desirable that sufficient erasing can be achieved with one operation of the erasing head. Furthermore, as a measure against the re-recording effect, it has been proposed that the erasing head has a double-gap structure, but as the track width becomes smaller, it is actually difficult to manufacture a head with this structure. Erasing using a DC magnetic field does not produce a re-recording effect, but has the disadvantage of generating even-order harmonic distortion in the next recording, so AC erasing is desirable. In this case, the erasing frequency needs to be sufficiently higher than the signal frequency as described later, but when the signal frequency is in a high frequency region, it is difficult to make the erasing frequency higher than this. For example, if the signal frequency band is
When extending up to 7MHz, the cancellation frequency should be at least
It is necessary to set the magnetic field to 7 MHz or higher, but core loss occurs in such a high frequency region, making it difficult to generate an erasing magnetic field large enough for erasing. Therefore, long wavelength signal components recorded deeply in the thickness direction of the recording medium cannot be erased, and power consumption also increases due to core loss. In order to avoid the above disadvantages, if the erasing frequency is set low and within the band of the signal component, the erasing magnetic field will be recorded and remain on the recording medium, and the signal component will include cross-modulation and even-order harmonics. produce defects. The component that remains after this erase magnetic field is recorded on the recording medium (hereinafter referred to as the erase component) is generally subject to losses such as recording demagnetization due to the erase magnetic field being excessively large compared to the optimum magnetic field for normal signal recording. Although it may be smaller than the signal component, it is at an extremely large level from the perspective of erasure rate. For the above reasons, erasing using a specific frequency within the signal band is inappropriate as a general erasing means. Purpose of the Invention The present invention eliminates the above-mentioned drawbacks of conventional erasing devices, erases only the magnetic signal of a predetermined track without unnecessary erasing adjacent tracks, and does not adversely affect the next recording or reproduction. The purpose of the present invention is to provide an erasing device without any A further object of the present invention is to provide an erasing device which achieves the above-mentioned object and is equipped with an erasing head having a gap length suitable for achieving this object. Structure of the Invention In order to achieve the above object, the present invention provides an erasing device capable of erasing magnetic signals recorded over a large number of tracks on a disc-shaped recording medium, one track at a time. When erasing is performed by the erasing head, erasing is enabled over an area that protrudes from the width of the track, and of the protruding area, erasing is enabled on the inner circumferential side of the track. Then, the length d by which the gap formed in the erasing head extends toward the inner side of the disc-shaped recording medium with respect to the gap formed in the recording or reproducing head is r _nio −√ ² _nio −〓 ² ≦ d<r _nax −√( _nax −〓) ² −〓 It is configured to satisfy the formula ² . Here, r _nio is the innermost radius of circular recording, r _nax is the outermost radius, 〓 is the gap distance between the erasing head and the recording or reproducing head, and 〓 is the guard band width. Hereinafter, with reference to the drawings, specific examples of the erasing device of the present invention, erasing frequency in the erasing device of the present invention,
The azimuth angle, the head gap, the width of the erasing head, and the mounting structure of the head in the erasing device of the present invention will be explained in detail. Specific examples of the erasing device of the present invention (Figs. 1 to 3)
Figure) Figure 1 schematically shows an example of an erasing device embodying the present invention, in which 1 is a track to be erased, 2 is an adjacent track, 3 is an erasing head, and 3g
is the gap, 4 is the track after erasing, and W is the width of the signal track. The erase head 3 has its erase coil supplied with an erase current from an erase signal source (not shown), and generates an erase magnetic field as is well known. The feature of this invention is that there is an azimuth angle between the track direction of the head gap 3g and the direction of the erased track 1, and furthermore, in this example, the track width of the erase head 3 represented by the track 4 after erasing is , is wider than the track width of the recording or reproducing head (not shown in this figure), represented by the signal track width W. To explain the erasing characteristics of the device shown in FIG. 1, there is an azimuth angle between the track direction of the erased track 1 on which a signal is recorded and the head gap 3g, that is, the erasing track, which is a factor that affects the erasing rate. The above-mentioned re-recording effect will be reduced due to the azimuth loss La.
In other words, the azimuth loss La (dB) is determined by the signal track width W (m), the azimuth angle (rad), and the signal wavelength
(m) is expressed by the following formula. La=−20log ₁₀ 〓Sin(πw〓/〓)/πw〓/〓〓
...(1) Fig. 2 is a graph showing equation (1), and in the figure, the solid line indicates the relationship of equation (1), which periodically has a maximum value. The dashed line in the figure shows the envelope La′ of the peak value in equation (1), and La′ is La′=−20log ₁₀ (1/πw〓/〓) (However, πw〓/ 〓＞〓/2 …( 2) Next, regarding the characteristics when an erased track is played back by a playback head, if the erase frequency is set within the signal frequency band, the erase magnetic field is recorded on the recording medium and the above-mentioned It remains as an erased component and has had a negative effect on signal reproduction characteristics in the past.However, according to the present invention, since the erased track and the reproduced track have an azimuth angle, this erased component causes azimuth loss during reproduction and is therefore reduced. The mode is shown in Fig. 3. In the figure, 4 is a track after erasing, 5 is a playback head,
5g indicates the gap, and the direction of the gap 5g coincides with the direction of the recording signal track, that is, the reproduction track, and the erase track 4 and the reproduction track have an azimuth angle . Therefore, the elimination component is
It decreases due to the azimuth loss La shown in (1) and FIG. In this case, ≦ in equation (1) represents the wavelength of the erased component. Erasing frequency in the erasing device of this invention (Fig. 4) The above-mentioned azimuth angle is determined by the signal track width, the signal wavelength or the erasing wavelength, and the required azimuth loss La.
It is determined from. The erasing frequency, azimuth angle, head gap, and track width of the erasing head will be explained in detail below. First, regarding the erasing frequency, assuming that the recording signal is an image signal, the distribution of signal frequency bands is normally as shown in FIG. 4. Here, 6 indicates the color signal band, which is distributed approximately between 200KHz and 2MHz.
Further, 7 indicates a luminance signal band, which is distributed approximately between 3 and 10 MHz. Therefore, the erasing frequency should preferably be selected to be 10 MHz or higher, but it is not possible to generate a sufficiently large magnetic field due to high frequency loss within the core, making it impossible to erase especially low-frequency signals. . Therefore, in order to be able to sufficiently cancel even the low frequency signals, the cancellation frequency needs to be at least 5MHz or less, but if the cancellation frequency is set within this band, the cancellation component will be recorded, and the above-mentioned Failures such as cross-modulation occur as shown in According to this invention, the erasure component can be reduced by azimuth loss during reproduction, but the degree of reduction is approximately 20 dB, as will be described later.
It cannot be completely erased. Therefore,
It is desirable that the cancellation frequency be set within a range such that even if a cancellation component exists, its influence will not occur as much as possible. For the above reasons, in relation to the recording signal having the frequency band distribution shown in FIG. 4, it is possible to set the erasing frequency between 2 and 3 MHz. This region corresponds to between the chrominance signal band and the luminance signal band of the image signal, and the signal component does not exist, or even if it does exist, the level is low, so the effect of the cancellation signal on the overall signal component is small. There is no problem in practice. According to research conducted by the inventors, it has been found that the erased component in this boundary region does not affect signal processing of images, etc. even when the signal component is about -20 dB. Azimuth angle (second
Figure) Regarding the azimuth angle in the specific example of this invention, focusing on the cancellation component, the cancellation frequency is
3MHz, so if the relative speed V (m/s) between the recording medium and the erasing head is determined, the erasing wavelength is determined.
Azimuth loss can be calculated from equation (1). As can be seen from the solid line in FIG. 2, when W, 〓 is constant, the azimuth loss has a maximum value with respect to 〓. Therefore, if the azimuth angle is selected so that the azimuth loss is maximized, a large loss can be obtained with a small azimuth angle. The azimuth angle that satisfies this condition is 〓=n・〓/π・w(rad) (n=1, 2,...
…) is given by (3). However, in a rotating disk-shaped recording medium, the radial position and circumferential speed differ depending on the track, so even for the same erasing frequency, the erasing wavelength differs depending on the track. Therefore, as can be seen from equation (3), the azimuth angle at which the azimuth loss is maximum also differs from track to track, so it is not possible to utilize the maximum value of the azimuth loss for all tracks. As a countermeasure against this, it is possible to calculate the azimuth loss using the envelope shown by the broken line in FIG. 2, assuming the worst case. However, as shown in the figure, as 〓 increases, the increase in azimuth loss slows down, so from the perspective of effectively utilizing azimuth loss, it is appropriate to set the azimuth loss to about 20 dB. . The table below shows an example of azimuth angle settings.
generally relative

[Table] Since the speed may change, the azimuth angle can be approximately within the range of 5 to 25 degrees. On the other hand, the deeper the azimuth angle, the higher the erasing rate, but if the azimuth angle is too deep, contact with the head (a state in which the head is in contact with the recording medium while maintaining parallelism, or is in contact with the recording medium at an interval of 50㎓ or less) may occur. It becomes a problem. According to experiments, it has been confirmed that the optimum azimuth angle is approximately 12 degrees when the track width is 60 mm, and approximately 22 degrees when the track width is 30 mm. Head gap in the erasing device of the present invention In embodying the present invention, the head gap should be characterized in that recording demagnetization is likely to occur (at least the wavelength must exceed the erasing wavelength), that erasing can be performed deep within the recording medium, and that re-recording is effective. From the viewpoint of reducing the gap as much as possible (increasing the gap as much as possible), it is allowed to be equal to or greater than the erasing wavelength or the thickness of the recording medium. On the other hand, from the viewpoint of ensuring stable contact with the head and reducing the erase current, it is preferable that the gap be as small as possible. Normally, the thickness of the medium on which VTR signals are recorded is 2 to 6 m, and if the relative speed is 6 m/s, the erasure wavelength is 2.4 m, and considering the above conditions, the gap is 4 to 8 m. m is appropriate. Further, it is desirable that the track width be wide in consideration of mechanical precision and off-track characteristics. Gap length of the erasing head in the erasing device of the present invention When the erasing device of the present invention is applied to a rotating disc-shaped magnetic recording medium such as a disk, the gap length of the erasing head in the erasing device of the present invention is It is desirable that the recording head and the recording or reproducing head be constructed integrally. In this case, if the gap lengths of both heads are the same, an off-track will occur corresponding to the curvature of the recording track and the gap distance of both heads.
This problem increases as the curvature increases, that is, as the circumference of the recording track decreases, making it impossible to perform satisfactory erasing. As a countermeasure for this, if a configuration is adopted in which the head is moved in accordance with the erasing track, the moving mechanism becomes complicated, and since the amount of movement varies depending on the recording radius, the mechanism becomes even more complicated. Therefore, the occurrence of off-track can be suppressed by increasing the length of the gap in the erasing head by d toward the inside of the disk relative to the gap in the recording or reproducing head. This length d is then limited by the curvature of the track. Hereinafter, the case of the innermost track and the case of the outermost track will be explained separately. In the case of the innermost track, in order to prevent off-track in the erase head, the gap length of the erase head extended by d must be located at the edge of the recording track or further inside. Here, the gap distance between the recording or reproducing head and the erasing head is 〓, and the radius of the innermost track is 〓.
If r _nio , then d can be found by finding a triangle obtained by moving the recording or reproducing head and the erasing head inside the disk by d. In other words, each side of the triangle is r _nio , 〓, r _nio − d, so r _nio − d=√ ² _nio − 〓 ² ∴d=r _nio −√ ² _nio − 〓 ^2Also , as mentioned above, The range of d can be longer than this length, so the range of d is d≧r _nio −√ ² _nio −〓 ^2On the other hand, in the case of the outermost circumference, there is a track on the inside, so the gap of the erase head is on the inside track. You have to make sure that it doesn't happen. Also,
A guard band is provided between the trucks. Considering the above, the width of the guard band is 〓, and the radius of the outermost track is _rnax , and the same way as the case of the innermost track can be considered.
Therefore, if we calculate each side of the triangle at this time, we get r _nax −〓, 〓, r _nax −d, so r _nax −d=√( _nax −〓) ² −〓 ² ∴d=r _nax − √( _nax −〓) ² −〓 ² Also, as mentioned above, it cannot be longer than this length, so the range of d is d<r _nax −√( _nax −〓) ² −〓 ² Since , d satisfies r _nio −√ ² _nio −〓 ² ≦ d＜r _nax −√( _nax −〓) ² −〓 ² . Therefore, by increasing the gap of the erasing head toward the inside of the disk with respect to the gap of the recording or reproducing head by an amount d that satisfies the above relational expression, off-track does not occur even if the erasing head is not moved, and a simple configuration is sufficient. Satisfactory erasure can be performed. Note that the upper limit to which the gap length of the erase head can be extended to the inside of the disk is limited by the width of the guard band, as described above. 〓: Gap distance between erase head and recording or playback head〓: By widening the track circle by d that satisfies the relationship of guard band width, off-track does not occur even if the erase head is not moved, and a simple configuration is sufficient. Satisfactory erasure can be performed. Note that the upper limit for increasing the width of the erase head inside the track circle as described above is limited by the width of the guard band. Note that the above example is a configuration for preventing off-track when using a rotating disk-shaped recording medium, and the means for achieving the main objective of the present invention are as follows.
It is sufficient to provide an azimuth angle between the erase track and the signal track to be erased. Mounting structure of the head in a specific example of the erasing device of the present invention (FIG. 5) FIG. 5 shows an example of the mounting structure of the erasing head and recording or reproducing head in the erasing device of the present invention. This is an example applied to In the figure, numeral 11 shows a part of the drum around which the magnetic tape is wound in a VTR, numerals 12 and 13 are the cores of the erasing head and recording or reproducing head, respectively, and gaps 12g and 13g are the gaps of the erasing head 12. It is assumed that there is an azimuth angle between the track direction of the gap 12g and the track direction of the magnetic signal to be erased.
The distance between the gaps 12g and 13g is 〓 as described above. Reference numeral 14 denotes a flexible support plate that supports both heads, and the support plate 14 is fixed to a rotating support bar (not shown) with mounting screws 15. Incidentally, magnetic head devices having the same structure as those shown in the figure are fixed to the rotation support bar at symmetrical positions with respect to the center of the drum 11, and these magnetic head devices rotate in the direction of arrow A in the figure. 16 and 17 both indicate eccentric pins, and by operating these, gaps 12g and 13g are created.
The spacing therebetween or the relative position of the symmetrically located magnetic head device to the head gap can be adjusted. Effects of the Invention As explained in detail above, by using the configuration according to the present invention, off-track does not occur even without moving the erasing head, and only the signal of a predetermined track can be erased without unnecessary erasing of adjacent tracks. can do.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the state during erasing of a specific example of the erasing device of the present invention, FIG. 2 is a diagram explaining azimuth loss, and FIG. 3 is a schematic diagram showing the state of a specific example of the erasing device of the present invention during reproduction. FIG. 4 is a schematic diagram showing the state, FIG. 4 is a diagram showing the frequency band distribution of the image signal, and FIG. 5 is a plan view showing an example of the mounting structure of the erasing head and the recording or reproducing head in the erasing device of the present invention. In the figure, 1...Track to be erased, 2...Adjacent track, 3...Erasing head, 3g...Gap, 4...Track after erasing, 5...Reproducing head, W...Width of signal track. =...Azimuth angle between the erase track and the signal track to be erased.

Claims (1)

[Scope of Claims] 1. An erasing device capable of erasing magnetic signals recorded over a large number of tracks on a disc-shaped recording medium track by track, wherein the recorded magnetic signals are erased by the erasing head. When erasing is performed, the erasing head is made to be able to erase over an area that protrudes from the width of the track, and in order to enable erasing on the inner circumferential side of the track among the protruding areas, an eraser is formed on the erasing head. The gap formed in the recording or reproducing head is defined such that a length d extending toward the inside of the disk-shaped recording medium satisfies the following formula: ^An _erasure ^device _that ^{_ _} _{_ _} is the gap distance between the erasing head and the recording or reproducing head, and = guard band width.