JPS5845097B2 - Capacitive video disc playback needle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a reproducing needle that relatively scans a track of a disc-shaped recording medium in which an information signal is recorded as a change in geometric shape and reproduces the information signal as a change in capacitance. By forming the electrode for detecting the information signal on the side surface extending in the same direction as the tangential direction to the track in the reproducing needle, the width of the electrode can be made extremely narrow. It is possible to reproduce high-density recorded recording media, reduce the stress on the electrode parts, improve reliability against damage to the electrode parts, and furthermore provide long life with excellent mass production. An object of the present invention is to provide a capacitive video disc playback needle having the following features.

An example of a conventional capacitive video disc playback needle is shown in FIGS. 1 and 2A, B, and C.

A reproducing needle 1 is attached to a video disc 2 rotating at high speed in the direction of arrow A, relatively scanning an information signal track 3 on the upper surface of the video disc 2, and picking up the information signal with an electrode 4.

The playback needle 1 has an electrode 4 on the upper back surface in the scanning direction relative to the video disc 2, and a pair of symmetrical surfaces 5 on the back surface side.
a, 5b, a pair of symmetrical surfaces 6a, 6b are formed on the front side, and a diamond-shaped disk contact surface 8 is symmetrical with respect to a virtual center line 7 in the relative scanning direction.

The video disc 2 is of a grooveless type, and has a configuration in which an information signal track 3 is formed by a main information pit 9 and a tracking reference pit 10 adjacent thereto, and the playback needle 1 is detected from the reference pit 10. The tracking error is corrected in accordance with the reference signal obtained, and the information signal is reproduced from the main information pit 9.

The regenerated needle 1 has the following shape characteristics.

(1) The electrode 4 is formed on the ridgeline of the open end side where contact with the contact surface 8 of the video disc 2 is released.

(2) The disk contact surface 8 has a width W1 and a length in the scanning direction which are considerably increased to have a wide area.

(3) As shown in FIG. 2A, the electrode 4 spreads at an angle α (>0) from the tip of the regeneration needle toward the base.

(4) The disk contact surface 8 has a sharp angle on the introduction side and has a symmetrical shape with respect to the center line in the disk scanning direction.

Looking at the above-mentioned characteristics, the regenerated needle 1 has some advantages, but it also has the various disadvantages described above.

First, in Patent 1), as the video disk is played back, the electrode 4 peels off from the main body of the playback needle, and the end face of the electrode becomes rounded and worn, making stable playback of information signals impossible.

That is, stress concentration occurs at the end of the playback needle that is out of contact with the disk, and a considerable amount of thermal energy is generated due to the attachment scanning.

Furthermore, the disk portion with which the needle is in contact is subjected to a certain pressure (for example, when the load of the needle is 60 mm and the base area is 25 μm2, the pressure is 2.4 kg/my?t), and its surface becomes slightly elastic. Since the disk is considered to have been deformed, when the disk passes through the bottom surface of the reproducing needle and is released from the pressure, it returns elastically, and at this time, an impact force is applied to the lower end surface of the electrode 4.

As a result, rounded wear may occur on the lower end surface of the electrode 4, and in some cases, the electrode 4 may peel off from the regenerated needle body.

That is, the lower end of the electrode 4 is damaged, making it impossible to stably reproduce the information signal.

Regarding feature (2), the needle pressure (load/area) can be reduced, wear is reduced, and the needle life can be extended, and the pressure acting on the disk can be reduced to prevent damage to the signal track. has.

However, on the other hand, the electrode 4 is also related to the formation part of the electrode 4.
The rising phenomenon from the disk signal surface becomes noticeable, causing level changes in the reproduced signal and making it unstable.

That is, in an actual playback apparatus, during disk playback, the video disk 2 in contact with the playback needle 1 changes in the vertical direction as shown by the solid line and the dashed-two dotted line in FIG.

This is caused by undulations on the disk surface, uneven thickness of the disk,
(Distance between the disc and the cantilever fulcrum) Due to error.

In this case, the reproduction needle 1 is displaced in the same direction as the disk 2 is displaced in the vertical direction, accompanied by the swinging of the cantilever 11.

FIG. 3 shows an enlarged view of the contact state of the playback needle 1 with the video disc 2 in this case, that is, the portion indicated by the solid line X in FIG. 3.

In the figure, virtual straight lines 2a, 2b, and 2c indicate the disk surface relative to the reproducing needle 1, respectively.

When the disk 2 is tilted so that the portion facing the reproduction needle introduction side is lowered, the disk surface becomes as shown by 2a, and the contact between the electrode 4 and the disk is maintained.

However, on the contrary, if the disc 2 is inclined so that the part facing the reproducing needle introduction side is higher, the disc surface will become as shown by 2b and 2c, and the reproducing needle 1 will be placed on the introduction side. contact the disk surface, and the electrodes 4 rise above the disk surface by distances S1 and S2, respectively.

However, during the reproduction operation, a phenomenon occurs in which the electrode 4 rises above the disk signal surface, and as a result, the reproduction signal level fluctuates.

Note that this lifting phenomenon is caused by the dimension Ll (
The longer the contact length (in the scanning direction) is, the more significant the problem becomes.

The solution to this problem must be to flatten the disc and improve the mechanical precision of the playback device, but this is extremely difficult and no safe solution can be expected.

Feature (3) is designed to facilitate electrode formation and polishing. By having the above-mentioned opening angle α, the electrode width B increases as the disk contact surface 8 wears, and the adjacent Crosstalk is more likely to occur from tracks that are worn, and there is less margin for wear.

This problem becomes more noticeable as the density of video discs increases.

Finally, feature (4) is designed to remove dust adhering to the disk surface during playback, and the disk contact surface 8 is shaped like a rhombus that is bilaterally symmetrical with respect to the center line 7 in the relative scanning direction. In order to do this, there are many surfaces to be polished on the sides of the recycled needle body, and the amount of polishing on both sides must be delicately controlled to ensure that the left and right sides are exactly the same. This makes polishing difficult and reduces mass productivity. There is a problem with this, and furthermore, there is a drawback that chipping occurs and the defective rate increases.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to the drawings.

FIG. 5 is a perspective view of one embodiment of the reproducing needle according to the present invention, seen from the back side, FIG. 6 is a diagram showing the relationship between the disc contacting surface of the reproducing needle and the video disc signal track, and FIG. 7 is a reproducing needle. FIG. 3 is a side view of the needle.

The capacitive video disk playback needle 20 has a playback needle main body 21 having a substantially rectangular bar shape, and a side surface 22 extending in the disk scanning direction, that is, in the tangential direction Y to the signal track.
The structure is such that an electrode 23 is formed on a part of this side surface 22.

The diamond or sapphire regenerated needle body 21 is defined by an introduction side surface 24, a back surface 25, side surfaces 22.degree. 26 on both sides, a surface 27 extending diagonally in a diagonal direction of the square rod, and a right triangular bottom surface 26. The shape is the same.

In this S, surfaces 23, 25 and 27 are finished to a mirror surface.

The bottom surface 28 is a mirror surface obtained by polishing off the top portion indicated by the two-dot chain line in FIG. 5 after forming the above-mentioned inclined surface 21.

The scanning direction dimension L2 of the bottom surface 28 is set to 10 to 15 .mu.m, and the disc radial direction dimension W2 is set to 5 to 8 .mu.m, which is larger than the pitch of the signal tracks described later.

Further, in FIG. 6, 29 is a signal track on the video disc 2, and p is a signal track pitch.

Arrow Y indicates signal track 2 at the position of electrode lower end 23a.
9 shows the tangential direction.

Here, the side surface 22 is a surface whose lower ridgeline is a ridgeline 29 extending in the direction of the arrow Y in the bottom surface 28, and extends in the direction of the arrow Y and perpendicular to the surface of the video disc 2. There is.

Further, the electrode 23 is formed by sputtering Hf, Ti, etc., and then by dry etching to form a constant width strip portion 2 having a constant width of a predetermined dimension W3 from the bottom surface 28 to a height position of a predetermined dimension H1.
This is 3b.

Further, the electrode 23 is formed by sputtering, so that its thickness W4 is considerably thin (for example, 5ooA
degree) and is formed in a well-controlled manner.

In this process, the thickness W4 of the extremely small rectangular electrode lower end 23a corresponds to the signal track pitch direction, and the width W3 corresponds to the signal track longitudinal direction.

Further, the constant width strip portion 23b is arranged at a position where the dimension L3 from the rear surface 25 of the regenerated needle main body is 1/3 to 1/2 of the total length L2 of the bottom surface.

Next, the capacitive video disc playback needle 2 having the above configuration
The state during video disc playback operation of No. 0 will be explained in comparison with the conventional example described above.

When playing a video disc, the video disc 2 has a playback needle 20.
It is slightly elastically deformed at the part attached to the bottom surface 28, and after passing through the bottom surface 28, it elastically returns to its original state.

In this construction, since the constant width strip portion 23b of the electrode 23 is formed on the side surface 22 of the playback needle main body 21 parallel to the scanning direction, the lower end portion 23a of the electrode is not affected by the impact of the elastic recovery of the video disc 20.

Further, thermal energy associated with scanning is not concentrated on the lower end portion 23a of the electrode.

That is, the mechanical destructive force acting on the electrode part is small, and the electrode 23
The lower end 23a of the constant width strip 23b does not become rounded due to wear, and this part
Further peeling does not occur.

As a result, the part of the electrode 23 that picks up the signal is not damaged due to the relative attachment scanning operation with respect to the disk, the reliability of the reproducing needle is improved, and the information signal is stably reproduced.

Note that the mechanical impact force acting on the electrode 23 on the side surface 22 may be caused by scratches on the disc surface, dust attached to the disc surface, etc., but these may be caused by improvements in disc mastering, pressing, etc. This problem can be solved by adopting a dust-proofing method for the disk.

Furthermore, if a surface runout occurs on the disk 2 or a height error occurs in the feeding of the playback needle in the disk radial direction, the signal surface of the disk 2 will be aligned with the virtual straight lines 2d and 2e in FIG. The bottom surface 28 is partially raised above the disk surface.

Incidentally, the bottom surface 28 is worn away by the disk 2 by performing attachment scanning with respect to the disk 2, and becomes a curved bottom surface 30.

However, in the regenerated needle 20 of the present invention, the lower end portion of the electrode 23, that is, the signal detection portion 23a is located at the bottom surface 30.28.
Since the disc 2 is located approximately at the center in the scanning direction, even if the disc 2 is extremely tilted as shown by the virtual straight lines 2d and 2e, the amount of floating above the disc signal surface is quite small.

Therefore, when the video disc 2 is rotating with normal surface wobbling, the signal detection part 23a of the electrode 23 scans the disc signal surface relatively while maintaining attachment to the disc signal surface without rising above the disc signal surface. do.

As a result, the signal detection ability of the playback needle 20 is not degraded by the surface runout of the video disc 2, and a playback output whose output level is kept substantially constant is obtained.

Further, in the reproducing needle 20, the bottom surface 28 has a dimension L2 of 10 to 15 μm and a dimension W2 of 5 to 8 μm, and its area is considerably large, so that the amount of wear caused by the disk reproducing operation is small.

Further, the strip portion 23b whose middle and lower end portion of the electrode 23 serves as the signal detection portion 23a is formed to have a constant thickness W4 and width W3 and to extend over a length (height) Hl, so that the wear of the bottom surface 28 is prevented. Even as the signal detecting section 23a progresses, the track pitch direction dimension W4 of the signal detecting section 23a remains unchanged.

As a result, the regeneration needle 20 has a considerably long life, and the signal detection characteristics are maintained in the initial state over the usable period, and problems such as crosstalk do not occur.

Furthermore, in the electrode 23, the dimension W4 corresponding to the signal track width of the video disc 2 is its thickness dimension.

In this case, the electrode 23 is formed by sputtering Hf or Ti, and its thickness is extremely thin (
For example, about 500 A) and is set with high precision.

Therefore, the playback needle 20 of the present invention has the ability to satisfactorily playback even video discs in which signal tracks are recorded and formed at an ultra-high density, and has an excellent effect in response to the trend towards ultra-high density video discs. demonstrate.

In addition, since the electrode 23 is formed with the desired thickness W4 to be extremely thin and with high precision, it is formed appropriately in accordance with the signal track width of the video disc, so that the playback needle for the desired video disc can be adjusted. This can be easily obtained by simply changing the sputtering conditions.

Further, the electrode strip portion 23b is formed to have a scan direction dimension W3 as small as about 0.5 μm by applying recent LSI device technology such as a pattern shape using an electron beam and a dry etching process.

The dimension W3 of the signal detection section 23a is related to the signal detection ability regarding frequency characteristics, but since the dimension W3 is set to about 0.5 μm, the playback needle 20 is
The information signal can be reproduced satisfactorily up to the innermost track without deterioration in frequency characteristics.

Further, the introduction side 28a of the inner bottom surface 28 of the playback needle 20 with respect to the disk has a sharp corner, and exhibits excellent dust removal ability.

In addition, in the reproducing needle 20, the surface 22 on which the electrode 23 is formed is formed perpendicularly to the disk surface, but the invention is not limited to this. The electrode 23 may be formed to be inclined at a predetermined angle from the surface, and the electrode 23 may be adhered to this inclined surface.

Next, a method for manufacturing the regenerated needle 20 is shown in FIGS.
This will be explained with reference to FIG.

8 to 10 show the electrode pattern forming process, and FIGS. 11 to 15 show the polishing process.

The regenerated needle 20 of the present invention also has superior features in terms of manufacturing method compared to conventional regenerated needle manufacturing methods.

FIG. 8 shows a sapphire plate 4 which is the base material of the recycled needle 20 of the present invention.
0, the desired flatness is achieved, and the thickness T is approximately 0.2
mm, and its negative surface 40a has a scratch-free mirror finish.

This surface 40aj is formed by chemical polishing, and the finish level is such that it can be applied to SO8 (silicon on sapphire), for example.

Next, in steps shown in FIGS. 9A to 9E, an electrode pattern shown enlarged in FIG. 10 is formed on the mirror surface 40a of the sapphire plate 40.

First, as shown in FIG. 9A, Ti is deposited on the mirror surface 40a of the sapphire plate 40 by means such as sputtering.
A titanium thin film 41 is formed.

This titanium thin film 41 is formed with its thickness precisely controlled, and this thickness ultimately becomes the electrode width dimension W4.

Next, as shown in FIG. B, PM is applied to the surface of the titanium film 41.
An electron beam sensitive agent such as MA is uniformly applied to form an electron beam sensitive agent coated film 42, and then this film 42 is patterned with an electron beam and developed.

As a result, only the necessary portions of the sensitizer film remain, as shown in FIG.

By patterning using the electron beam, about 100 predetermined electrode patterns are deformed at a predetermined pitch.

Next, the exposed titanium thin film 41 is removed by dry etching such as plasma etching in an atmosphere of reactive gas CF4+02 (approximately 2%).

This results in the state shown in the figure.

Finally, the remaining sensitizer coating film 42 is removed to obtain a desired titanium electrode pattern 43, as shown in FIG.

Since electron beam patterning and dry etching are applied here, a large number of titanium electrode patterns 43 having minute widths and deep etching depths can be easily formed simultaneously.

Note that when this titanium electrode pattern 43 is enlarged, it is the 10th
The result will be as shown in the figure.

The plurality of electrode patterns 43 are arranged at intervals of about 0.2 mm in consideration of the width of the later slicing process.

Looking at the shape of the electrode pattern 43 in this process, the lower strip 43a, which is an important part of the electrode, has a constant width of width W3 and is formed to be long and extend over a height) H2 (>Hl). be.

Moreover, the striped portion 43a has a predetermined dimension L from the ridgeline 43d of the pattern.
It is formed in position 3.

The wide portion of the electrode portion 43b is formed with a width W5 of 0.2 mm and a length E of approximately 1.5 mm.

Further, the lower edge 43c of the wide electrode portion 43b is inclined in consideration of the needle-shaped appearance after completion of processing.

In this case, the above-mentioned pattern formation is performed automatically, and there is no problem in the mass production of recycled needles.

Next, the sapphire plate 40 on which the electrode pattern 43 is formed as described above is sliced with a diamond blade in correspondence with the electrode pattern 43 to form a needle tip 5 as shown in FIG.
Cut out 0.

In this S, the needle tip 50 is attached to the rear ridge line 4 of the electrode pattern 43.
Slice processing is performed with a predetermined polishing allowance F (20 to 50 μm) remaining for 3d.

This is because the chipping of the slice surface 0a itself is quite large.

Next, the sliced surface 50a is polished, the polishing allowance is removed, and the polished surface 5 coincides with the pattern ridge line 43d.
1 to obtain a needle tip 52 shown in FIG.

This polishing process is easily performed by electrically controlling the amount of polishing.

Further, this polishing process is performed by lapping process using diamond abrasive grains having a diameter of 1/4 μm (nominal) and 5n-Pb wrap, and the polished surface 51 is made to be a scratch-free surface.

Further, the facing surface 53 of the polished surface 510 is also lapped, and the needle tip 52 is made to have a predetermined width dimension W6 (=, W5).

Note that the roughness of the surface 53 is not important in terms of the characteristics of the regenerated needle.

Next, as shown in FIG. 13, in the needle tip 52, the electrode strip 4
The ridgeline 52a near 3a and the ridgeline 52b on the diagonal side thereof are positioned and inclined in a virtual vertical plane, and the tip thereof is lapped with a horizontal plane 54 shown by a two-dot chain line in the same figure.
A needle tip 56 having a diagonally inclined abrasive surface 55 as shown in FIG. 4 is obtained.

The inclined polishing surface 55 is a scratch-free mirror surface.

In addition, regarding the polishing process to obtain the polished surface 55, since it is sufficient that the striped portion 43a remains, simple time management is sufficient to control the amount of wear.

Finally, the lower tip of the needle tip 56 is polished to form a mirror-like bottom surface 57 as shown in FIG.
(20) is obtained.

In order to obtain the regenerated needle 58 (20), the mechanical polishing process only needs to be performed on four sides, and symmetry is not required. Since no control is required, this method is much simpler than conventional recycled needle polishing and is convenient for mass production.

As described above, according to the capacitive video disk playback needle of the present invention, the electrode for detecting the information signal of the video disk is arranged in the playback needle main body in the same direction as the tangential direction to the signal track at the playback needle attachment position. Since it is formed on the side surface extending in the direction, there is less stress concentration on the signal detection part of the electrode during video disc playback.
Therefore, accidents in which the signal detection part of the electrode is damaged can be eliminated, and signal detection can be performed stably.Also, since the thickness direction of the electrode corresponds to the track width direction, the track width of the electrode can be eliminated. The size can be set extremely small, and it can respond to the trend towards higher density recording of video discs.Also, since the playback needle body does not need to be symmetrical with respect to the center in the scanning direction, the required polishing surface can be reduced. The number of electrodes can be reduced, and the control of the amount of polishing does not require as much precision as in conventional methods, and the polishing process can be easily performed, making it suitable for mass production. By arranging it so that it is located approximately in the center, even if there is a disturbance such as disk surface wobbling, it is possible to almost eliminate the floating of the signal detection part of the electrode from the disk surface, and the information signal can be maintained at a stable level. It has excellent features such as being able to be played back.

[Brief explanation of the drawing]

Fig. 1 is a diagram schematically showing a state in which a conventional video disc playback needle is attached to a video disc, and Fig. 2 A-
C is a front view of an example of a conventional video disc playback needle;
A side view and a bottom view. FIG. 3 is a diagram showing changes in the attachment state of the video disc playback needle to the disc as the video disc changes in the height direction. FIG.
FIG. 5 is a perspective view of an embodiment of the capacitive video disc playback needle according to the present invention, and FIG. 6 is a diagram showing the disk contacting surface of the playback needle shown in FIG. 5. An enlarged view, FIG. 7 is a side view of the regenerated needle shown in FIG. 5, and FIG.
The figure shows the sapphire plate that is the base material of the recycled needle in Figure 5, Figures 9A to E are diagrams showing the electrode pattern manufacturing process for the sapphire plate in Figure 8, and Figure 10 shows the electrode pattern. The enlarged views, FIGS. 11 to 15, are diagrams showing the polishing process for the needle tip. 2...Video disc, 3,29...
Information signal track, 20.58... Capacitive video disc playback needle, 21... Playback needle body,
22...Side surface, 23...Electrode, 23a
・・・・・・Lower end of electrode (signal detection part), 23b...
... constant width stripe, 28, 30, 57 ... bottom surface,
29...Ridge line, 40...Sapphire plate, 41...Titanium thin film, 42...Electron beam sensitizer coating film, 43... Titanium electrode pattern, 43a...Striped portion, 50, 52, 56...
... Needle tip, 55 ... Inclined polished surface.

Claims (1)

[Scope of Claims] 1. A reproducing needle that relatively scans tracks of a disc-shaped recording medium in which an information signal is recorded as a change in geometric shape and reproduces the information signal as a change in capacitance. A capacitive video disc playback needle, characterized in that an electrode is formed on a side surface of the playback needle main body extending in the same direction as the tangential direction to the track at the playback needle attachment position. . 2. The capacitance type video according to claim 1, wherein the electrode is disposed in the side surface so as to be located approximately at the center in the scanning direction of the disk contact surface of the playback needle. Disc playback needle.