U.S. patent number 3,654,401 [Application Number 05/041,281] was granted by the patent office on 1972-04-04 for playback system with radiation guide member having a slide portion extending into the groove.
This patent grant is currently assigned to Licentia Patent-Verwaltungs-G.m.b.H.. Invention is credited to Helmut Batsch, Gerhard Dickopp, Eduard Schuller.
United States Patent |
3,654,401 |
Dickopp , et al. |
April 4, 1972 |
PLAYBACK SYSTEM WITH RADIATION GUIDE MEMBER HAVING A SLIDE PORTION
EXTENDING INTO THE GROOVE
Abstract
An improved system for reproducing signals stored on a recording
medium in the form of undulations corresponding to the signals, the
undulations generally being formed as a spiral groove. The
undulations on the recording medium are moved past a suitable
radiation source, such as a light source, and the density of the
radiation emanating from the undulations, which is a function of
the curvature of the undulation, is detected by a suitable
radiation detecting means after it passes through a suitable slit
aperture arranged at a predetermined distance from the recording
medium surface so that variations in the density are a function of
the undulations. The undulations may be either frequency or phase
modulated with respect to the signal and their amplitude can be
modified as a function of their recorded wavelength in such a
manner that the curved surface portions of the undulations have
nearly the same focal length for all occurring wavelengths. The
tracking of the playback system is improved by providing a
radiation guide member which slides along the raised portions of
the surface of the recording medium and has a slide member which
extends into the particular groove or portion thereof being
scanned. Formed within the guide member is an element which is
optically effective for the type of radiation utilized to collect
the emanating radiation and aids in its evaluation. This element
may be either the slit aperture itself or a collecting lens which
directs the emanating radiation to the slit aperture.
Inventors: |
Dickopp; Gerhard (Berlin,
DT), Batsch; Helmut (Berlin, DT), Schuller;
Eduard (Berlin, DT) |
Assignee: |
Licentia
Patent-Verwaltungs-G.m.b.H. (Frankfurt, DT)
|
Family
ID: |
5735535 |
Appl.
No.: |
05/041,281 |
Filed: |
May 28, 1970 |
Foreign Application Priority Data
|
|
|
|
|
May 29, 1969 [DT] |
|
|
P 19 27 408.9 |
|
Current U.S.
Class: |
369/18;
G9B/7.097; 369/111; 369/112.23; 369/61 |
Current CPC
Class: |
G11B
7/12 (20130101) |
Current International
Class: |
G11B
7/12 (20060101); G11b 003/34 (); H04r 023/00 () |
Field of
Search: |
;179/1.3V,1.41L,1.6M
;178/6.6A,6.7R,6.7A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Konick; Bernard
Assistant Examiner: Cardillo, Jr.; Raymond F.
Claims
We claim:
1. In a system for playing back, by means of a beam of parallel
light radiation, signals recorded in the form of a carrier
frequency which is frequency or phase modulated with the signals
and within a groove or grooves on the surface of a recording medium
by means of undulations of said surface corresponding to the time
sequence of the signal values, wherein said record medium is moved
relative to said beam of light radiation and wherein a slit
aperture and said surface bearing the undulations are disposed in
the path of said beam of radiation at such a distance from one
another that a change in the density of the radiation emanating
from the surface bearing the deformations results in the plane of
the slit aperture, said change in density being dependent on the
undulations existing on said surface in the direction of the
relative movement of the recording medium and said reading beam and
which change in density at least qualitatively reproduces the
course of the undulations, and wherein means are provided behind
said slit aperture for detecting the radiation passing through said
slit aperture; the improvement comprising: radiation guide means
positioned in the path of said beam of said radiation, said guide
means including a slide member which extends into the particular
groove or portion thereof on said surface of said record medium
from which it is desired to play back the recorded signal, said
guide means including means optically effective for the type of
radiation employed for aiding in the evaluation of the light
density fluctuations produced in said particular groove.
2. The playback system as defined in claim 1 wherein said optically
effective means is said slit aperture which extends through said
guide means.
3. The playback system as defined in claim 1 wherein said optically
effective means is a lens arrangement which reproduces the plane of
evaluatable primary light density variations directly produced by
the undulations in a second plane bearing corresponding secondary
light density variations, whereby said secondary light density
variations can then pass through said slit aperture to said
detecting means.
4. The playback system as defined in claim 1 wherein the sides of
said guide means which are adjacent the neighboring grooves are
provided with a radiation-impermeable coating.
5. The playback as defined in claim 1 wherein said guide means is
provided with laterally extending surfaces for contacting the
raised portions of said surface forming the walls between adjacent
grooves, and wherein said slide member engages the groove profile
with lateral play and extends into said groove to such a distance
that the base thereof does not touch the groove bottom bearing the
undulations.
6. The playback system as defined in claim 5 wherein said optically
effective means is a slit aperture which is constructed to be
clearly permeable for the type of radiation employed and comprises
two parallel bordering surfaces which are disposed perpendicular to
the direction of relative movement between said guide means and the
surface of the groove being scanned, said bordering surfaces being
portions of said guide means, and being substantially centrally
located between the peripheral surfaces of said guide means.
7. The playback system as defined in claim 6 wherein said slit
aperture takes up a central spatial portion within the outline
surfaces of said guide means.
8. The playback system as defined in claim 7 wherein an objective
lens is provided in the path of said reading beam of radiation
between the outlet of said slit aperture and said detecting means
for producing an intermediate reproduction of the slit aperture
outlet, the aperture of said objective lens being so dimensioned
that when a slit aperture with well reflecting bordering planes is
used the outer beams of the reading beam bundle of rays which exit
under acute angles with respect to the optical axis of the reading
beam bundle are covered over the entire permissible fluctuation
range of the position of the guide element with respect to the
groove being scanned in both the axial and radial directions.
9. The playback system as defined in claim 6 wherein the length of
said slit aperture is not larger than one-half of the shortest
recorded wavelength, wherein the width of said slit aperture is
approximately equal to the width of the recorded undulations.
10. The playback system as defined in claim 9 wherein the depth of
said slit aperture is substantially greater than the length thereof
and wherein said bordering surfaces of said slit aperture have good
reflecting properties.
11. The playback system as defined in claim 6 wherein said slit
aperture is filled with a solid transparent material which is
permanently connected to said bordering surfaces and with the
adjacent portions of the guide means.
12. The playback system as defined in claim 11 wherein said
transparent material has an index of refraction such that total
reflection results along said bordering surfaces in the usable
range of the optical impingement angles occurring at the slit
aperture entrance.
13. The playback system as defined in claim 5 wherein said
optically effective means is a lens arrangement which reproduces
the plane of evaluatable primary light density variations directly
produced by the undulations in a second plane bearing corresponding
secondary light density variations, whereby said secondary light
density variations can then pass through said slit aperture to said
detecting means, and wherein said lens arrangement contains a
condensor lens whose image length is selected to be greater than
the object length.
14. The playback system as defined in claim 13 wherein at least the
portion of said guide means which is disposed in the path of said
beam portion to be evaluated consists of a material which is
clearly permeable for the radiation.
15. The playback system as defined in claim 14 wherein said lens is
a cylindrical lens.
16. They playback system as defined in claim 14 wherein the clearly
permeable portion of said guide means bears a collector lens on its
side facing away from said record medium, with the axis of said
lens being perpendicular to the direction of relative movement of
said guide means with respect to the undulation-bearing groove
surface being scanned.
17. The playback system as defined in claim 16 wherein the length
of said slit aperture is at least approximately equal to one-half
of the shortest recording wavelength contained in the undulations,
multiplied by the enlargement factor between said plane of the
primary light density variations and said plane of the secondary
light density variations.
18. The playback system as defined in claim 17 wherein the width of
said slit aperture is substantially larger than the width of the
light track in said plane of the secondary light density
changes.
19. The playback system as defined in claim 18 wherein said
detecting means is mechanically connected with said slit aperture.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This invention relates to an improvement of the invention disclosed
and claimed in copending application Ser. No. 5,341,235 filed Jan.
23, 1970, by Gerhard Dickopp.
BACKGROUND OF THE INVENTION
The present invention relates to an improved system for playing
back signals stored on a recording medium whose surface is provided
with deformations or undulations which correspond to the time
sequence of the signal amplitude by means of light radiation or a
radiation related thereto and a radiation detector.
According to the above-mentioned copending related patent
application, the signal values are recorded in the form of carrier
frequency oscillations having the signal frequency- or
phase-modulated thereon, and playback is achieved by means of a
slit aperture which, together with the surface bearing the
undulations are disposed in the path of the radiation beam at such
a distance from one another that a change in the density of the
radiation emanating from the surface bearing the undulations
results in the plane of the slit aperture. The change in density is
dependent on the undulations existing on the surface bearing the
recorded signals in the direction of the relative movement of the
record medium with respect to the reading beam bundle of rays and
is at least a qualitative reproduction of the course of the
undulations.
While the basic playback arrangement provided in the
above-mentioned patent application for such a system operates
satisfactorily under optimum conditions there still remain some
practical difficulties which have not been overcome satisfactorily.
These difficulties arise due to the need for improvement in the
basic arrangement of the means for maintaining the optical system,
which cooperates with the reading beam bundle of rays, on an even
track and for vertically guiding of the optical system. The term
"maintaining an even track" is intended to mean that only the
signal from a single groove is evaluated and crosstalk from
adjacent grooves is prevented. In order to maintain an even track,
it is necessary that the reading beam system follow the signal
track recorded in the associated groove even when this groove
occasionally performs lateral movements with respect to the reading
beam system as, for example, might happen with a so-called radial
wobble of the recording medium in disc or foil shape. The vertical
guiding of the carrier or recording medium in disc or foil shape
with respect to a slit aperture or an optical system containing
such an aperture must be such that, at the occurrence of a
so-called vertical wobble of the carrier, the fluctuating component
of the evaluated light flux changes as little as possible, or in
any case that a sufficiently large fluctuating component of the
light flux is always received even with the greatest practical
occurring differences in height.
SUMMARY OF THE INVENTION
It is the object of the present invention to overcome these
difficulties which occur in a practical realization of the basic
system according to the above-mentioned copending patent
application and to provide an arrangement for such a system in
which it is possible to positively keep the scanning system on an
even track with reference to the associated groove and assure
satisfactory vertical guiding during vertical movements of the
carrier.
The above object is achieved in that, in a system for playing back,
by means of a beam of light radiation or radiation related thereto,
stored signals recorded in the form of frequency- or
phase-modulated carrier frequency oscillations on a carrier or
recording medium whose surface contains undulations corresponding
to the time sequence of the signal values, wherein a slit aperture
and the surface bearing the undulations are disposed in the path of
the reading beam at such a distance from one another that a change
in the density of the radiation emanating from the surface bearing
the undulations, which change in density is dependent on the
undulations existing on the surface of the recording medium in the
direction of relative movement of the recording medium with respect
to the reading beam and at least qualitatively reproduces the
course of the undulations, occurs in the plane of the slit aperture
whereby it can then be received by the radiation detector,
according to the present invention, a radiation guide means is
provided which has a slide member which extends into the particular
groove of the recording medium bearing the undulations to be
scanned and which contains an element which is optically effective
for the type of radiation employed and aids in the evaluation of
the light density fluctuations produced from the associated
groove.
The guide means is preferably provided with two laterally extending
slide surfaces intended to contact the raised portions existing
between adjacent grooves and with a slide member engaging the
groove profile with lateral play and having the base thereof not
physically engaging the groove bottom which bears the
undulations.
According to one embodiment of the present invention, the optically
effective element is the slit aperture of the optical system.
According to another embodiment, the optically effective element
may consist of a lens arrangement which reproduces the plane of
evaluatable primary light density fluctuations directly produced by
the undulations of the recording medium surface in another plane
which exhibits corresponding secondary light density fluctuations,
i.e., the plane of the system slit aperture. The slit aperture
which may be in the form of either an air gap or a clear,
transparent optical body of the same dimensions as the air gap,
while the lens arrangement -- which contains a condenser lens or
which is a condenser lens -- is selected so that the image length
is larger than the object length in order to produce an enlarged
reproduction of the plane (object plane) containing the light
density fluctuations produced directly by the deformations in
another plane (image plane). In both embodiments, the slit aperture
or the lens arrangement are preferably contained in substantially
the central portion of the guide means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation illustrating the basic
playback arrangement according to the present invention.
FIG. 2 is an enlarged view of a guide means according to one
embodiment of the invention illustrating the operative relationship
between the guide means and a portion of the recording medium with
the undulations in a groove thereof.
FIG. 3 is a schematic representation illustrating a slit aperture
for the guide means according to one embodiment of the invention
and the terminology employed for the dimensions of the slit
aperture.
FIG. 4 is an enlarged view of the path of the radiation between a
radiation source and the radiation receiver, with total reflection
of the laterally impinging radiation occurring within the slit
aperture.
FIG. 5 is a representation, similar to FIG. 2, of another
embodiment of the invention showing a portion of the recording
medium, a groove and a guide element moving therein, the latter
being combined with a condenser lens.
FIG. 6 is an enlarged view of the beam path when using a guide
means having a condenser lens according to FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1 there is shown a schematic representation
of the improved playback system according to the invention. As
illustrated in the figure, the recording carrier or medium is a
circular disc 1 mounted for rotation about an axis 2. The disc 1,
which in the illustrated embodiment is transparent, is preferably
formed from a synthetic material which is formable at a temperature
higher than the operating temperature. Formed on the surface of the
disc 1 when it was in its formable state are a plurality of grooves
3 having undulations at the bottom thereof which contain the signal
recording applied in the manner disclosed in the above-mentioned
copending application, i.e., frequency- or phase-modulated carrier
frequency oscillations. In order to read and evaluate the signals
contained in the undulations the radiation source 4 is disposed on
the one side of the carrier which, during signal playback, rotates
about axis 2. The output radiation from source 4 is directed
through a lens system 5 to produce a plurality of parallel rays 13
which are directed to one side of the disc 1, which in the
illustrated embodiment is the underside of the disc 1. The parallel
rays 13 perpendicularly strike the planar underside of disc 1 so
that there is no deflection of the rays at that point, and
penetrate the disc, which is clearly permeable for the type of
radiation employed, and exit on its upper side. The portions of the
bundle of rays 13 which are penetrating through the undulations in
the shape of lenses (preferably cylindrical) disposed transverse to
their direction of travel and containing the signal recording are
condensed or dispersed, depending on the curvature of these lenses,
in a plane disposed above the signal recording track so that
variations in the radiation density which correspond to the course
of the signal occur in this plane. These variations are now
converted, for a selected track, by an optical system into
variations of light intensity. The radiation receiver or detector 6
is excited by the exiting light flux 14, whose intensity is now
modulated corresponding to the signal course, and converts the
changes in radiation into appropriate changes of an electrical
output value (not shown).
According to the invention, in order to maintain an even track with
respect to the radiation emanating from the upper surface of disc 1
and to allow proper vertical guiding of the optical system with
respect to the radiation to be evaluated, a radiation guide element
or member, which is generally opaque, is provided to guide the
above-mentioned optically effective element (not shown in this
figure) which aids or takes a significant part in the evaluation of
the light density variations, always in the proper position with
respect to the undulations contained in the particular groove 3
being evaluated. According to the preferred embodiments of the
invention, the guide element 7 contains the optically effective
element utilized in evaluating the light density variations
produced by the undulations of the associated groove 3. Preferably
an opaque covering member 8 is provided, in the path of the reading
beam bundle of rays 13 to shield the radiation receiver 6 against
scattered light. To achieve this result the covering member 8 is
provided with an opening (not shown) in the area of the optically
effective element, for the passage of the useful light flux, and
extends laterally beyond the sidewalls of the guide member 7.
In order to provide the desired guiding function for the optical
system, the guide element 7 is provided with laterally extending
slide or bearing surfaces 16 which slide on the raised portions 11
of the upper surface of the disc 1 defining the walls between
adjacent grooves 3, and with a slide member 15 which extends into
the particular groove whose signal is being evaluated and engages
the groove profile with lateral play. The bottom portion of the
member 15 only extends into the groove 3 a distance such that it
does not contact the portion of the groove bearing the undulations,
preferably the bottom of the groove. This construction of the guide
member 7 assures that even when the disc 1 experiences vertical
and/or lateral wobble, the guide element 7 performs the respective
movements of the groove 3 being scanned with great approximation,
so that the lateral position of the optically effective element,
which may for example be a slit aperture, with respect to the
particular groove being scanned and also its distance from the
groove surface containing the signal recording hardly ever changes
during operation.
FIG. 2 shows a greatly enlarged representation of a portion of
recording carrier or disc 1 with a groove 3 which bears in its
bottom the undulations 12 containing the signal recording. In the
manner disclosed in the related above-mentioned copending patent
application these undulations preferably form cylindrical
collecting and diverging lenses which cause variations in the
density of the beam bundle of rays in a plane a short distance
above their vertex. The direction of relative movement of the guide
element 7 with respect to the groove surface of carrier disc 1 is
indicated by the the arrow d.
As already discussed above in connection with FIG. 1, the guide
element 7 in this embodiment is provided with laterally extending
slide surfaces 16 which slide on the upper sides 11 of the walls
defining the grooves 3, and the slide member 15 extends into and
engages the groove profile with lateral play. This play is
necessary at this location because with inclined groove sides there
would otherwise occur a static redundancy of the guiding process.
The figure illustrates a position for the slide member 7 in which
it is in contact with the left side of the groove whereas the
lateral play or clearance can be seen at the right side.
According to the embodiment illustrated in FIG. 3, the optically
effective element contained in the guide element 7, which in this
embodiment is opaque, is a slit aperture 9. The movement of the
guide element 7 with respect to carrier disc 1 causes the slit
aperture 9 and its entrance opening to be passed through the plane
of density variations of the particular track or groove being
evaluated so that a light flux of varying intensity enters into the
aperture slit entrance. This light flux passes through the slit
aperture 9 and exits from the exit opening of the slit as modulated
light flux having rays 14, from where it is brought to the
radiation receiver 6, not shown in this figure.
The slit aperture 9 is constructed to be clearly permeable for the
type of radiation employed, and is formed by two parallel bordering
surfaces e which are disposed perpendicular to the direction of
relative movement of the guide element 7 with respect to the
adjacent surface of groove 3 and which borders on portions of the
guide element 7. Preferably the slit aperture 9 takes up a central
portion within the peripheral surfaces of the guide element 7, so
that relatively slight displacements of the slit aperture 9 with
respect to the track occur when the guide element performs tipping
movements.
As indicated above, the slit aperture 9 may take a number of
different forms. One type of slit aperture, i.e., an air gap, is
illustrated in FIG. 3 which will be utilized to explain the general
criteria and dimensions for the slit apertures to be included in
the guide element 7 according to the invention.
Referring now to FIG. 3, there is shown a schematic representation
of an air gap type of slit aperture disposed between adjacent
portions of guide element 7. The slit aperture has the spatial
shape of a parallelepiped whose major limiting surfaces
simultaneously form the adjacent end surfaces of the components of
the guide element. The length of the gap in the direction of
relative movement d of guide element 7 with respect to the
recording carrier is marked l. This slit length l should not be
larger, according to known dimensioning principles, than one-half
the length of the shortest recorded wavelength of the signal track
to be scanned, reference being made to the side at which the signal
track is reproduced in the plane of the slit aperture entrance.
With direct scanning of a signal track recorded according to the
refined high-density recording technique the slit aperture length l
is approximately 1.5 to 2.mu.m.
The gap width a of the slit aperture is the dimension thereof lying
in the same direction as the width of the track, i.e., undulations
to be scanned. This width a--again with reference to the
reproduction in the plane of the slit aperture entrance--should
generally be equal to the track width.
The light permeability of a slit aperture does not depend only upon
its cross-sectional dimensions, the rectangle with the sides l and
a, but substantially also upon its depth c. This is particularly
true when the radiation does not always impinge on the slit
aperture entrance at a right angle. The entrance of perpendicular
light, however, is possible in approximation only for the rays near
the axes of the quasi-cylindrical lenses which form the undulations
containing the signal recording. A substantial portion of the light
flux entering into the slit aperture does, however, not originate
from the perpendicularly impinging rays. The slit aperture must
thus be so constructed, in order to provide good utilization of the
light flux, that the light entering thereinto over a certain
angular range also exits therefrom. This is the case, in
approximation, when the slit aperture depth c is no greater than
the slit length l, or when, with a relatively great slit depth c
the slit-delineating surfaces e reflect so well that only slight
damping of the light occurs even when multiple reflection occurs
between the two surfaces. In the case of well-reflecting
delineating surfaces, the scanning slit aperture may be disposed
directly in the guide element 7 which takes over the groove
guiding. Utilizing a larger slit depth c results in the advantage
that the system still remains able to function after the guide
element 7 has been worn through use. The light entrance plane of
the slit aperture must be able to be displaced within a certain
tolerance range while still allowing a sufficiently large,
fluctuating component of the light flux to pass through the slit
aperture in the direction of the axis of the reading beam bundle of
rays 13. For video signals recorded in the high-density recording
technique this tolerance range is, for example, up to 10 .mu.m.
To produce a minimum of reflection losses at the border surfaces e
of the slit aperture several possibilities are presented. One such
possibility is the metallic mirroring of the bordering surfaces e.
Since the reflection capability of metallic mirrors is a maximum of
0.96 to 0.98, a 20-fold reflection already produces a loss of more
than 50 percent. Such silvering is therefore only appropriate when
the slit aperture depth e is not larger than 20 times the slit
aperture length l, i.e., in the case of video signals recorded in
the high-density recording technique, less than 30 to 40.mu.m. This
requirement makes the production of such a slit aperture
difficult.
A further and advantageous possibility consists in the utilization
of the phenomenon of total reflection at the bordering surfaces e.
In this case the light loss occurring due to reflection is very low
so that even after several thousand reflections only a slight
intensity loss occurs. A prerequisite for the occurrence to total
reflection is that the material contained in the slit aperture be
optically denser than the surrounding medium. Such an embodiment of
the invention is in fact illustrated in FIG. 2, and the operation
thereof explained with the aid of FIG. 4.
Returning again to FIG. 2, as illustrated the slit aperture
containing a solid member 9' -- hereinafter referred to as a "slit
member" -- which is permanently connected at the bordering planes e
with the adjacent portions of the guide element 7. The material
employed for the slit member 9' has such an index of refraction
that total reflection results in the useful areas of the optical
angles of incidence at the slit aperture entrance along the
bordering planes e. In this case, the slit depth c of FIG. 3 may be
selected to be substantially larger than if the system were to
operate without total reflection at the bordering planes.
The optical requirements for total reflection are that the material
of the slit member 9' be optically denser than the surrounding
medium. A glass foil having a high index of refraction, e.g.,
n.sub.1 = 1.7 may be inserted into the center portion of the opaque
guide element 7 by means of an adhesive 17 or by means of a glass
solder having a low index of refraction, e.g., n.sub.2 = 1.5. The
slit member 9' then acts as a light conductor for all the light
which in the case of the above-mentioned indices of refraction
impinges on the slit entrance surface at an angle of 36.degree. to
90.degree.. For a difference in the indices of refraction of 0.1,
the permissible angular range is still sufficient for the impinging
light rays.
In order to protect the slit member 9' or the guide element 7,
respectively, against the impingement of light from adjacent tracks
or grooves through which the bundle of rays 13 of the reading beam
passes, the guide element 7 is provided with lateral coatings 10
which have good reflecting properties on their side facing the
guide element 7 or the slit member 9', respectively, but are
impermeable to the radiation impinging from the outside.
FIG. 4 shows an illustration of the beam path for an arrangement
according to FIG. 2, i.e., with a slit aperture containing a slit
member 9'. Corresponding portions of FIGS. 2 and 4 are provided
with the same reference numerals. FIG. 4 shows only the portions of
the guide member 7 bordering on the slit member 9' or the adhesive
17, and carrier or disc 1 is shown only as a section through the
groove bottom. From the figure it can be seen that the portion of
the reading beam bundle of rays 13 which comes from the radiation
source passes through carrier 1 and that periodic variations in the
radiation density occur in a plane x -- x which are produced by the
recorded signal wave represented by the undulations 12, the plane x
-- x lying in the vicinity of the entrance opening of slit member
9'. The direction of relative movement between the slit member 9'
and carrier surface is again indicated by the arrow d. The entrance
opening of slit member 9' now covers light fluxes of varying
density in the plane x -- x with the illustrated case being that in
which the density covered by the slit aperture is a maximum. The
axial ray of the portion covered by the slit member 9' passes
directly through the center of the slit and of the subsequently
disposed lens 18, i.e., without being reflected at the bordering
planes e, and travels to radiation receiver 19. The outer beams are
totally reflected several times at the bordering planes e of the
slit member 9' and then exit from the slit plane under exiting
angles which are equal to the corresponding entrance angles. These
exiting rays then go to lens 18 from where they are directed to
radiation receiver 19.
It should be noted that the light flux coming from the optically
effective member of the guide element is guided to the radiation
receiver 6 of FIG. 1, or 19 of FIG. 4, respectively, in different
ways. In FIG. 1, the radiation receiver is disposed directly behind
the exit side of the member contained in guide element 7. This
necessitates a reduced distance between the radiation receiver and
the guide element which can not always be realized constructively
in a simple manner. In FIG. 4 a second possibility is shown in
which a lens 18 produces an intermediate reproduction of the slit
exit at the input of the radiation receiver 19. The aperture of
this lens is so dimensioned that, when a slit aperture is used
which has well-reflecting border planes, the outer beams which exit
at acute angles with respect to the optical axis of the reading
beam bundle of rays are covered in both the axial and radial
directions over the entire permissible fluctuation range of the
position of guide element 7 with reference to the track. This is a
prerequisite for the minimum aperture of the lens. However, the
aperture of the lens 18 should not be selected any larger than
necessary so that the laterally impinging, interfering scattered
rays are not registered. Since only the magnitude of the total
light flux is registered by the radiation receiver, no sharp
reproduction of the slit aperture exit side is necessary. Thus a
vertical wobble of carrier 1 has no influence on the useful signal
even if it leads to a change in the width of the object. The only
prerequisite is that the entire photo flux be received by the
radiation receiver over the entire fluctuation range.
A further possibility for guiding the light flux from the output of
the slit member 9' to the input of the radiation receiver 19 would
be to employ an advantageously flexible light conductor. Such light
conductors are sufficiently well known in the art so that a further
description thereof is not required. The input of such a light
conductor could be directly connected with the slit exit and its
output directly connected to radiation receiver 19 to form the
input thereof.
In the arrangement whose details were described in connection with
FIGS. 2 and 4, the guide element 7 together with slit member 9' as
well as an intermediate optical system, if required, in the form of
lens 18, and radiation receiver 19 are advantageously forced to
move along the radius of the disc-shaped carrier 1. Radial and
axial wobble of the carrier can be absorbed by spring-suspended
supports for the above-mentioned parts so that these parts can move
along corresponding to the particular wobble. This is not
absolutely necessary, however, for lens 18 and radiation receiver
19 so long as the lens diameter and the area of the input of
receiver 19 are large enough so that in spite of the wobble the
total light flux exiting from the slit aperture can always be
received.
FIGS. 5 and 6 describe an alternate embodiment of an arrangement
according to the present invention in which the optically effective
member which is connected with the guide element 7 is a lens
arrangement which represents the plane of the evaluatable primary
light density fluctuations directly produced by the deformations in
another plane which exhibits corresponding secondary light density
fluctuations. As shown in FIG. 5, which is a representation similar
to that of FIG. 2, where corresponding portions bear the same
reference numerals, the guide element 7 bears a condenser lens 20
on its upper surface. The sides of guide element 7 which are
adjacent the adjacent grooves are provided -- as in FIG. 2 -- with
a radiation-impermeable coating 10. Contrary to the embodiment of
FIG. 2, at least the portion of guide element 7 which is disposed
in the path of the radiation portion to be evaluated, or the entire
guide element, is formed of a material which is clearly transparent
for the radiation. Since the guide element should have good sliding
characteristics together with low wear, at least at the slide
surfaces 16, it may consist of a suitable optical glass, a sapphire
crystal or a diamond crystal. The guide element 7 may consist of a
connected piece of such a material so that the entire element acts
as a cylindrical lens. It is, however, also possible to fabricate
the guide element 7 to initially have a plane covering surface and
then to glue on a cylindrical lens. Instead of a cylindrical lens
it is also possible to use a spherical lens. The cylindrical lens,
however, is better suited for the problem to be solved and exhibits
the advantage that it is easier to manufacture, for example, from a
glass filament. The axis of this cylindrical lens 20 is positioned
perpendicular to the direction of the relative movement d between
guide element 7 and the surface of groove carrier or disc 1. Thus
the axis of the cylindrical lens 20 is parallel to the axes of the
quasi-cylindrical lenses forming the undulations in the bottom of
the grooves. With the aid of cylindrical lens 20 the plane of wide
light density fluctuations, which is marked x -- x in FIG. 6, is
reproduced in a plane in which the slit aperture of the system is
disposed or which is closely adjacent to the slit aperture, the
reproduction occurring with simultaneous enlargement, e.g., by the
factor 10. The length of the slit aperture should then be
approximately equal to one-half of the shortest recorded wavelength
multiplied by the optical enlargement factor of the cylindrical
lens. The width of the slit aperture may be substantially larger
than the width of the image of the track in the slit aperture
plane.
The slit aperture plane and the radiation receiver are advisably
forced to move along a radius of the disc-shaped carrier
corresponding to the inclination of the groove. The guide element
which is present in the shape of a cylindrical lens may be
resiliently fastened to the forcibly moved arrangement so that it
can follow the radial and axial wobble of the carrier. The width of
the receiving slit aperture 9 should be large enough so that the
image of the track is always covered by the slit even when there is
a radial wobble. Crosstalk from adjacent grooves is avoided by the
above-mentioned coating 10 on the guide element 7 of FIG. 5.
FIG. 6 is a greatly enlarged illustration of the beam path of an
arrangement according to FIG. 5. This illustration is similar to
that of FIG. 4 and corresponding portions bear the same reference
numerals. It can be seen that the parallel bundle of rays 13 of the
reading beam are either condensed or dispersed, as in FIG. 4, by
the undulations 12 of carrier or disc 1 so that periodic density
fluctuations of the radiation result in the plane x -- x (which is
here disposed inside the transparent guide element 7). From this
plane x -- x of density variations the cylindrical lens 20 produces
in slit plane y' -- y' an enlarged image by appropriately directing
the exiting beams 14. Thus the length l of slit aperture 9 in this
plane may be larger by the enlargement factor than if this slit
were disposed in plane x -- x. The radiation receiver 6 may be
combined with slit aperture 9 and guide element 7 into a mechanical
unit.
FIG. 6 illustrates that the object length g for the condenser lens
20 is selected to be substantially smaller than the image length b
in which the image of the secondary light density fluctuations is
produced (y -- y).
With axial wobble the plane of optium light density variations,
which is shown in FIG. 6 in approximation as the plane x -- x, is
also displaced in an axial direction. The distance between it and
the cylindrical lens 20, however, remains unchanged due to the
contact of the guide element with the disc surface. The distance
between lens 20 and the slit aperture 9, however, does change. The
range of focus for image plane y -- y is greater, however, with an
enlarged reproduction than that for the object plane x -- x, i.e.,
by a factor equal to the square of the enlargement. As indicated in
the related above-identified patent application sufficient light
density fluctuation is present over a vertical range of
approximately 5 to 10.mu.m when reference is made to the
dimensional relationships of the high-density recording technique
for video signals. This numerical value thus applies for
wavelengths of about 4.mu.m and amplitudes of about 0.5.mu.m. With
an enlargement factor of 10 there thus results a corresponding
range for the image plane y -- y of 0.5 to 1 mm. If the carrier
wobble remains within this range, a sufficiently large fluctuating
portion of the light flux will always pass through the slit
aperture 9. This condition can thus be met without too many
difficulties.
The use of an enlargement is thus advantageous for two reasons:
firstly, the slit aperture becomes easier to manufacture because
its dimensions can be enlarged and secondly, the range of focus
within plane y -- y is increased.
With the relatively wide range of focus for the object plane of 5
to 10.mu.m it is assured that slight vertical fluctuations of the
cylindrical lens with respect to the carrier surface, as they might
be caused by the deposition of dust particles, will have hardly any
interfering effect. The reproducing lens in the indicated
arrangement follows each vertical and lateral wobble of the
carrier. Wear of the guide element 7 on the slide surfaces 16 can
be compensated by appropriate vertical adjustment of the receiving
slit plane (slit aperture 9).
It will be understood that the above description of the present
invention is susceptible to various modifications, changes and
adaptations, and the same are intended to be comprehended within
the meaning and range of equivalents of the appended claims.
* * * * *