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Description 1, title of the invention
3. Detailed Description of the Invention In the known video disc system (DE 15 14 489), the
video signal, in the form of a frequency-modulated carrier, is a relief-like ridge along a spiral
track. It is memorized in the form. The scanning is carried out by means of a pressure scanner,
during which the scanning surface of the scanner remains largely stationary in the direction of
the force exerted by the ridge, while scanning each time. The ridge below the vessel exerts
pressure on the scanner as it is depressed. A pressure transducer is connected to the scanner,
which delivers the signal corresponding to the ridge in the form of a frequency-modulated
carrier. The scanner is then formed asymmetrically. The EndPage: 1 scanner has an edge surface
that is slightly inclined to the video disk surface, and a steep edge surface that stands
approximately perpendicular to the disk surface. The ridge then leaves the scanner at a surface
which is flat and substantially vertical. In this case, the pressure applied to the scanner is not
sudden and a signal corresponding to the output of the transducer is generated. In this case, the
flat edge on the approach side of the scanner is formed in such a way that the pressure increases
over the interval of 1 to 100 wavelengths, and the steep edge on the far side is within the
interval of at most half wavelengths. It is also known to form the pressure to drop to O (DE 20 24
539). During such pressure scanning, the transducer has the property that the amplitude of the
signal generated decreases with decreasing wavelength and thus with increasing wave number.
The wave number is proportional to the frequency when the reproduction speed is constant. This
property is described in detail in DE-A 25 47 431. In the given case this property is: It has been
found that the drop does not decrease continuously toward the higher wave number a, and drops
suddenly at a predetermined wave number. This reduces the 19 / N ratio at this wave number.
Such non-uniform wavelength characteristics have been found to be caused by the configuration
of the scanner and the mode of pressure scanning and are, at first glance, unavoidable. It is an
object of the present invention to improve the wavelength characteristics during the pressure
scanning and thus the S / N ratio of the signal obtained at the output of the converter. According
to the invention this problem is solved as follows. That is, the scanner is positioned with respect
to the direction of rotation of the video disc such that the ridges strike the second steeply edged
surface of the scanner. The ridges in the video disc groove hurry when scanning.
The scan according to the invention, which falls on the edge of the ridge, must be considered as a
simple cine. That is to say that during such scanning, unlike the prior art, the scanner acts like a
plane and destroys the video disc groove or at least reduces the groove life by a considerable
amount (3). Be done. However, it has been found that the increased wear of the video disc groove
is within acceptable limits and nevertheless offers many advantages over compensating for the
drawbacks which may result in the increased wear. In particular, the solution according to the
invention offers the following advantages: (1) First of all, it is possible to obtain continuous
wavelength characteristics without bending at predetermined wavelengths, and thus to obtain a
better S / N ratio. This is explained as follows. During a known scan in which the ridges ride on
the flat side of the scanner and leave the scanner at the steep edge face, pressure relief at the
steep edge face generates a signal at the output of the transducer. However, a friction component
is produced on the flat surface, which likewise produces a signal at the output of the transducer.
However, since the pressure component at the sharp edge and the friction component at the flat
surface act in the opposite direction to each other, the above-mentioned drop of the wavelength
characteristic (4) may occur at a given wavelength. In the solution according to the invention, the
pressure component acts on the steep edge surface, which generates the signal not by a pressure
relief but by a pressure rise, and the friction component is advantageously identical on the flat
edge surface. Act in the direction. The reduction that occurs at a given wavelength in known
systems thereby no longer occurs or decreases substantially. 2. In the inventive arrangement of
the scanner as described in more detail, the parallel position of the tube supporting the scanner
to the video disc is obtained. Such parallel position has the following advantages. If the tube is
inclined relative to the video disk as in the known video disk player, for example, the recess of
the video disk causes a vertical movement of the tube, which necessarily in the horizontal
direction and thus in the track direction. Movement of the scanner also occurs. However, such
motion necessarily distorts the scanned frequency. At this time, if the tube piece is parallel to the
EndPage: 2 with respect to the video disk, the vertical deflection of the tube piece causes
substantially no movement of the scanner in the track direction, so that the signal distortion is an
order of magnitude. Is avoided. In known scans where the ridges in the video disc groove reach
the scanner at the flat edge face, the wedge between the scanner and the video disc necessarily
results in the flat edge face of the scanner and the video disc The scanner, which tends to collect
dirt from the surface, tends to lift from the video disc groove and results in a contact pressure
drop at the scanning edge that is detrimental to the mode of pressure scanning, In this case, the
scanning edge is formed by a steep edge surface and a flat edge surface.
Therefore, when playing back a video disc, the contact force must be determined larger than
originally necessary to compensate for this effect. On the contrary, in the solution according to
the invention, the dirt which is in the video disk groove is displaced by the edge 9 of the steep
edge of the scanner and by this edge. No stagnation occurs between the flat side of the scanner
and the video disc groove. Because here the heights leave the scanner in a direction that no
longer contacts the flat surface. By reducing this dirt collection, the contact force of the scanner
on the video disc can be reduced for known players, in which the ridges of the video disc groove
ride up on the flat edge surface. This reduction in contact force, on the other hand, reduces the
wear of the video disc groove as desired. This advantage therefore counteracts the resulting
drawback of increased wear of the video disc groove. An embodiment of the invention will now
be described by means of the drawings. In FIG. 1, a scanner 1 made of diamond is connected to a
tube 4 via a pressure transducer 2 and a damping member 3, which is resilient to the radially
moving slide of the video disc. Is attached to The connection between the scanner 1 and the
transducer 2 is (7) glued or brazed by the seam 5. The scanner 1 has a flat edge surface 8
inclined at an angle α with respect to the plane surface of the video disk 7 and a steep edge
surface 9 inclined at an angle δ with respect to a line perpendicular to the video disk 6.
Including. The generation of the signal U1 at the output of the transducer 2 takes place by the
ridge 1o in the video disc groove 7 exerting a pressure pulse on the scanner 9. In the known
video disc player, the video disc is first raised in FIG. 1 from right to left in FIG. 1 from flat
surface 8 and then away from the scanner 1 at the steeply edged surface 9, where suddenly Is
driven to generate signal U1 by pressure relief. On the contrary, the feed of the video disc 7 is
not in this direction, but the ridge 10 first strikes the steeply edged surface 9 where the sudden
pressure response of the transducer 2 produces the signal U1 and is then flat It takes place at the
edge face 8 in a direction away from the transducer 1. Figure 2 shows position X. The curve of
the pressure P acting on the transducer 1 from the ridge 10 of the bidet (8) disc 7 is shown
between. The pressure at the center of the ridge 10 is at a maximum, which increases with the
increase of the crushing force of the ridge.
X o represents the point at which the ridge 1 G hits the steep edge face 9, and X 1 represents the
point at which the ridge 10 just no longer contacts the scanner 1. The curve 1.2 K shows the
progression over the mean value of the pressure response at rest. This curve gives rise to the
characteristic 13 during scanning, which does not already have a slight dent 141,2 +) at a given
wave number. The relationship shown by the broken line 15 is desirable for optimum
characteristics. A characteristic 13 with a recess 14 is shown in FIG. FIG. 3 shows how the
pressure relationship with respect to each position of the scanner changes in a known system. It
is clear that the curve 16 deviates from the curve 12 in a disadvantageous direction. As a result,
a characteristic 17 having a larger dent EndPage: 318 in the wavelength characteristic is
obtained. The indent 18 represents the variation of the useful signal at a given wavelength, and
hence the reduction of the S / N ratio. FIG. 4 shows the relationship of the average pressure
obtained in the solution according to the invention in the form of a curve 23. At this time, it is
apparent that the ideal relationship by the curve 15 of FIG. 2 is approximated. As a result,
uniform wavelength characteristics 19 can be obtained without any dents due to the above
reasons. Therefore, according to the present invention, the disadvantageous wavelength
characteristic according to the characteristic 17 of FIG. 5 is converted to the wavelength
characteristic 19 of FIG. Thereby, the S / N ratio is improved at least at a predetermined
wavelength. FIG. 6 once more shows the position of the scanner 1 in the track 20 of the video
disc 7. The flat edge surface 8 of the scanner 1 is ground by means of a grinding wheel lying in a
plane 21 indicated by a broken line. By means of the polishing foil whose scanner 1 is in the
plane 21, the tube 4 is parallel to the bead deode disc 7 Vc and there is no direction 11 caused
by the movement of the scanner 1 in the track direction. It is clear that it can be polished. During
a known scan in which the ridges in the video disc groove Z ride on the flat edge surface 8, the
flat edge surface 8 is inclined in the opposite direction at the parallel position of the tube 4 with
respect to the video disk 7 in FIG. It has to go down, so it has to go down to the right. It is clear
that at such an oblique position of the flat edge surface 8 the scanner 1 can no longer be
polished back. That is, at this time, the relatively large polishing foil collides with the tube 4. This
is because this special inclined surface 21 intersects the tube 4 at the left side of the scanner 2.
A later polishing of the scanner 1 by means of polishing foil is, for example, the German patent
DE 2053 866. It is explained in detail in the booklet.
4. Brief description of the drawings FIG. 1 shows the scanning scheme according to the invention,
FIGS. 2, 3 and 4 show normalized pressure distribution over the length of the scanner, 5 (12)
shows normalized wavelength characteristics corresponding to FIG. 2 to FIG. 4, and FIG. FIG. 7
shows the relationship between the scanner and the video disc to illustrate the advantages shown
in FIG. 1 scanner, 7 video disks, 8 flat edge faces, 9 steep edge faces, 10 · ridges, 11 rotation
direction EndPage: 4
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